Articles tagged “Z80”

I've been having a tricky time buying LM35DZ analogue temperature sensors for a project recently. One pair of probes and a bag of loose components labelled LM35DZ turned out to be regular NPN transistors with a fake label on them, and another pair of probes ended up being DS18B20 digital temperature sensors. Whilst the DS18B20 temperature sensors were useless for the project I had in mind they were still functioning components. These use the 1-Wire serial bus, a bus named for the way that its single data line can also be used to parasitically power the devices on the bus.

1-Wire BBC BASIC Electronics Z80 Z88

It's been quite a while since I posted about my Z80 Computer project. This is a home-made Z80 computer I built back in 2010 that features a 10MHz Z80 CPU with 64KB RAM that runs CP/M 3. It can drive an internal LCD, TV or VGA monitor at 320x240 (monochrome only) and unfortunately is a project I was never too happy with due to several compromises I had to make in its design – though at the time I was happy enough I got it to work at all! The video output was limited by both my choice to use an internal graphical LCD and the limitations of the dsPIC33F I chose to use to drive it and the software was all a bit half-baked.

CP/M Electronics Z80 Z80 computer

The previous release of the TI-83 Plus BootExec program relied on temporarily replacing TI's Silver Link driver with WinUSB if you wanted to use the Silver Link USB cable. I've updated the program so it will try to use TI's driver if it's available, or WinUSB if not. This should help people who can't (or don't want to) temporarily replace TI's driver. The updated application can be downloaded, as before, from the same link: ti83p-bootexec.zip.

TI-83+ Z80

This is a quick update to the TI-83 Plus BootExec program described in a previous journal entry. The program now supports the USB "Silver Link" cable (as well as the serial "Black Link" it previously supported) though to access the USB device you do need to temporarily replace TI's supplied driver with a generic WinUSB one which can be organised with Zadig. The updated application can be downloaded from the same link as before: ti83p-bootexec.zip.

TI-83+ Z80

A few years ago I started running into problems with my TI-83 Plus graphical calculator. I was unable to install applications – it would keep locking up when "defragmenting". In the end I attempted to reinstall the operating system to see if that would cure matters, but that failed too and in the process left the calculator in a state where it wouldn't boot at all. Switching it on you'd be presented with a screen prompting you to reinstall the OS:
Waiting... Please install calculator software now.

TI-83+ Z80

The VDrive is a handy module for electronic projects that need to access files on a USB flash drive. It's based around a USB host microcontroller and comes preinstalled with some firmware that provides control over the drive with simple commands sent via a serial connection (UART or SPI). A few years ago I started putting together some code to connect the module to my Cambridge Z88 computer. All I needed was a way to power the drive and a MAX232 chip to translate the computer's RS-232 interface to the VDrive's logic levels, and after around 150 lines of BBC BASIC I had a program that could show directory listings, let me browse folders, and fetch files from the USB drive to the Z88's file system.

Electronics USB VDrive Z80 Z88

One of the issues holding me back with my development of the Light Gun Commando project (aside from a lack of free time due to the day job) was running out of prototyping breadboards and the difficulty of swapping between different console adaptor boards for testing. Normally by this point I'd have started soldering together more permanent prototypes on little circuit boards, but I've been having a difficult time with the boards I've got in stock apparently being made of a metal that's impossible to solder to.

Electronics RetroWiFiModem TI-83+ TIWiFiModem Z80

More musing on tape phases I bought a few more Acorn-format BBC BASIC cassettes to test my adaptation of BBC BASIC to the Sega Master System with, and have found a few interesting oddities since my last post. In that post I made the assertion that the phase of the recorded signals on the tapes is at 180°, i.e. each wave cycle goes negative before it goes positive (whereas a 0° phase would go positive before it goes negative). This matched the documentation I'd read, the output of tools like PlayUEF and my own tests with commercially-recorded tapes.

BBC BASIC Electronics Sega Sega Master System Tape loader Z80

I have now moved the tape interface circuit described in the previous entry from its breadboard prototype to a neat enclosure where I am happy to report it mostly works as well as it did before. I have spotted two issues, though. The first affects my small cassette recorder but not the large one, and is related to reading files from tape via the file IO routines (such as OPENIN then BGET# to retrieve a single byte, not from LOAD). Files are stored on tape in 256 byte blocks, and when the file is opened a whole 256 byte block is read from the tape and copied to the Master System's RAM.

BBC BASIC Electronics Sega Sega Master System Tape loader USB VDrive Z80

It's been quite a while since my last post but work has continued with the version of BBC BASIC (Z80) for the Sega Master System. Most of the features I have been working have not been particularly exciting to write about on their own, but here are some of the notable changes:
All VDU code (for text and graphics output) has been moved to a separate ROM bank, freeing up around 16KB of extra ROM space. It makes calling the code slightly more complicated but in the previous post I mentioned that I had less than 100 bytes of free ROM space so this was definitely required.

BBC BASIC Electronics Sega Sega Master System Tape loader Z80

After I posted about the pattern filling modes on Twitter I was alerted to the BBC Micro Bot website which hosts a gallery of programs that produce impressive graphical output from very short BASIC programs (short enough to fit in a Tweet!)
I tried a few of them out but unfortunately ran into problems with a lot of them that use various tricks to reduce the original program text length by embedding non-ASCII characters directly into the body of the program. My usual approach to prepare programs was either to copy and paste them into an emulator (my emulator strips out non-ASCII characters on pasting, as these can't be mapped to keystrokes) or to save them to a file and transfer that serially, and my own editor's tokeniser and BBC BASIC for Windows both had a habit of mangling the non-ASCII characters.

BBC BASIC Cogwheel Sega Sega Master System Tape loader Z80

One of the features I was quite happy with in the TI-83 Plus version of BBC BASIC was the dithered fills used to provide some semblance of different colours. Sixteen different patterns were provided between black and white:
As well as baking in the sixteen different dithered patterns I added a command that let you use your own pattern tile in a very hacky method (you'd allocate the memory for the pattern via DIM and then pass the address of that memory to GCOLPAT – the extra "PAT" statement after GCOL is what did the trick).

BBC BASIC Sega Sega Master System Z80

I've made quite a few changes to the way colours and plotting modes are handled in the Sega Master System version of BBC BASIC; previously this was handled on a per-graphics-mode driver basis, but this resulted in a lot of duplicated code and some inconsistencies. The new code is a bit more straightforward but also adds quite a few new features, most obviously different plotting modes:
Plotting with the OR mode The above screenshot shows the result of filling three circles with the OR plotting mode.

BBC BASIC Sega Sega Master System Z80

The video display processor in the Sega Master System is derived from the TMS9918A and provides a number of different screen modes. These modes are mostly character-based and generate the picture that is displayed on your TV based on two blocks of data in video RAM: the name table, which specifies which character appears in each cell on the screen and the pattern generator which contains the pixel data for each character. TMS9918A "Text" mode The "Text" mode is probably the most straightforward example.

BBC BASIC Sega Sega Master System Z80

I have continued to work on the Sega Master System version of BBC BASIC, and it's feeling much more like a practical version of BASIC than something that was just holding together to run one specific program! One of the key improvements is to standardise the handling of the different graphics modes. Previously I was using a coordinate system where (0,0) is in the top left corner and all drawing operations were carried out using physical device coordinates (so the screen was treated as being 256 pixels wide and 192 pixels tall).

BBC BASIC Cogwheel Electronics Emulation Sega Sega Master System Z80

I've recently been spending some time finding a way to run BBC BASIC on the Sega Master System, inspired by BASIC Month 6: The Mandelbaum Set on the RetroBattlestations Reddit community. When this month's program was first announced I tried running it on my only unarguably retrobattlestation, my Cambridge Z88, but the screen's low (vertical) resolution didn't do the program much justice. I thought this gave me two options:
Control some external piece of retro tech to produce higher-resolution output (e.g.

BBC BASIC Electronics Sega Sega Master System Z80

The last piece of hardware to add to the computer was a parallel port. These have eight data lines and nine assorted control and status lines. My last two 8-bit I/O expanders provide sixteen of these seventeen lines, and the final one was provided by the DS1307 real-time clock chip which happily has a spare pin on it that can be used as an output. This parallel port can be used to print from the computer. Some software has printing capabilities built in (such as the text editor VEDIT Plus), but by pressing Ctrl+P in CP/M any text sent to the display will be simultaneously sent to the printer.

Comments CP/M Parallel port Printing Z80 Z80 computer

At the end of the previous entry I mentioned that I was going to start developing my own programs for the Z80 computer. The first is a graphical clock, taking advantage of my implementation of the BBC Micro's VDU commands and the ability to use those commands to draw graphics onto the screen as well as text:
I have uploaded the code and binary to my site for anyone who is interested, though it will only work on a machine running CP/M 3 and that is equipped with a display that implements a handful of BBC Micro VDU commands.

Comments Clock CP/M RS-232 Z80 Z80 computer

Work continues on the Z80 computer. The two final modifications to the box itself are the holes for the status LEDs and the power switch. The green LED indicates power and the orange one disk activity. Unfortunately, the project box is fairly scratched on the outside (one scratch on the front is my own fault, but the sides and back were fairly scuffed and scratched when I bought it). If anyone has any tips for polishing scratches out of ABS I'd be glad to hear them; the usual household polishing abrasives (such as toothpaste) remove most of the light scuffs and result in a lovely mirror finish, but don't do anything to the deeper scratches.

Comments Z80 Z80 computer

One of the fun things about working with electronics is that you can end up with a physical product at the end of your hard work. To this end I have started moving my Z80 computer from its current breadboard to a more permanent enclosure. Large project boxes can be quite expensive (around £40, it seems), but the one I picked out was a slightly more reasonable £7. It's not the prettiest enclosure I've seen but it should be large enough to house the computer and provide space on the lid for the LCD and on the rear surface for a collection of connectors (as you'd expect to find on the rear of any computer).

Comments Z80 Z80 computer

The ultimate goal for the video display controller module I have been working on is to drive the display in my Z80 computer project. As I have now got a pretty good set of features I thought it would be a good idea to join the two projects together. The big board in the lower middle of the above photograph is the main body of the computer, including the Z80, its RAM, the ATmega644P that is used to handle I/O, an SD card for storage and a DS1307 real-time clock. The small board in the bottom left of the photo is the power supply (supplying both 5V and 3.3V) and clock generator (providing a 20MHz and 10MHz clock).

Comments dsPIC33 VDC dsPIC33FJ128GP802 Electronics PIC Z80 Z80 computer

Up to this point I have been running CP/M 2.2 on the Z80 computer. CP/M 3 adds a number of useful features, including the following:
Support for more than 64KB RAM via banked memory. Standardised access to real-time clock for file date and time stamping.Improved text entry on the command-line when using the memory-banked version, such as the ability to move the cursor when editing and recall the previously entered line.Support for disks with physical sectors larger than the default record size of 128 bytes.

Comments ATmega644P AVR CP/M DS1307 Electronics SD card Z80 Z80 computer

The hardware for the computer has changed in (mostly) subtle ways since the last post, with the exception of a PS/2 socket for connection to a keyboard. PS/2 keyboards (which use the same protocol as the older AT keyboard) communicate with the host by clocking data in either direction (keyboard to host or host to keyboard) over two wires, appropriately named "clock" and "data". An AVR pin change interrupt is used to detect a change in state of the clock line and either input or output a bit on the data line depending on the current direction of data transmission.

Comments ATmega644P AVR CP/M Electronics Keyboard Z80 Z80 computer

I've been working on a new Z80 computer over the last few days. I would say that I had been working on the existing Z80 computer were it not for the fact that this a completely new design. The previous computer had two 32KB RAM chips to provide a total of 64KB RAM. To run a user program you need to get it into RAM somehow, so I also included a 128KB ROM chip which occupied the lower 16KB of the Z80's address space to provide the fixed operating system that could be used to load programs. By adding memory banking hardware I could select one of eight 16KB pages of ROM.

Comments ATmega644P AVR CP/M Electronics Z80 Z80 computer

It's been some time since I worked on my Z80 computer project, but the recent electronics projects I've completed have got me thinking about it again. Click to watch the video on YouTube I did record a video to demonstrate the basic parts of the computer and some of its flaws a few months ago, which can be seen above. However, I'm now thinking of a more radical redesign than fixing the I/O board's shortcomings. One of the reasons for my lack of motivation is that even if I did get something working I wouldn't have much software to run on it; it would be a lot of work to write software that only ran on that one particular machine.

Comments CP/M Electronics Z80 Z80 Computer

The expression evaluators I've written in the past have been memory hungry and complex. Reading the BBC BASIC ROM user's guide introduced me to the concept of expression evaluation using top-down analysis, which only uses a small amount of constant RAM and the stack. I took some time out over the weekend to write an expression evaluator in Z80 assembly using this technique. It can take an expression in the form of a NUL-terminated string, like this:
.db "(-8>>2)+ceil(pi())+200E-2**sqrt(abs((~(2&4)>>>(30^sin(rad(90))))-(10>?1)))",0 and produce a single answer (or an error!) in the form of a floating-point number.

Comments Z80

I've made a few additions to the operating system for the computer. The Console module, which handles text input and output, now supports "coloured" text - that is you can set the text foreground and background colours to either black or white. This functionality is exposed via the BBC BASIC COLOUR statement. If you pass a value between 0 and 127 this sets the foreground colour (0..63 is white, 64..127 is black) and if you pass a value between 128 and 255 this sets the background colour (128..191 is white, 192..255 is black).

Comments Spinning cube Z80 Z80 computer

The CHIP-8/SCHIP interpreter now seems happy enough to run games, though the lack of settings to control how fast or slow they run makes things rather interesting. First of all, I've hacked together a painfully simple read-only file system. Each file is prefixed with a 13-byte header; 8 bytes for the filename (padded with spaces), 3 bytes for the extension (padded with spaces) and two bytes for the file size. The above file listing can be generated by typing *. at the BASIC prompt. I've written a new sprite drawing routine that scales sprites up to double size when in CHIP-8 mode; this allows CHIP-8 games to fill the entire screen.

Comments CHIP-8 Z80 Z80 computer

The only major hardware modification since last time is the addition of another 32KB SRAM. Click to toggle labels This appears as two 16KB pages in the $4000..$7FFF slot. Currently only the first page is used for OS variables and scratch space, freeing up the upper 32KB entirely for BBC BASIC's use. One other minor hardware addition is support for a dual-coloured LED on the control port. This LED will be used to signify file access - reads by a green LED and writes by a red LED. As such I haven't implemented a proper file system, but typing SAVE "FILE" or LOAD "FILE" at the prompt will transfer data between the Z80 RAM and a 24LC256 32KB EEPROM.

Comments CHIP-8 Electronics Z80 Z80 computer

Dates, times and backlights
I'm using a DS1307 real-time clock to provide the computer with real-time date and time functions. It's a great little chip - all it needs is power, two lines for I2C communications, a 32768Hz crystal between two pins and a back-up battery to keep it ticking when main power is removed and it's happy. That accounts for seven pins; the last remaining pin can be used as a one-bit output (you can set it to a high or low state in software) or it can be configured to output a square wave at 1Hz, ~4kHz, ~8kHz or ~32kHz.

Comments BBC BASIC DS1307 Electronics Z80 Z80 computer

Cheers for the comments. As EasilyConfused pointed out, I have done calculator programming in the past, which makes this much easier - learning Z80 assembly to program a calculator influenced the choice of CPU in this computer, and porting BBC BASIC to the calculator showed that with a minimal amount of code to sit between it and the hardware you'd have a decent operating system with very little work. And if a Terminator-related name is good enough for the UK military, it should be good enough for this project...

Comments Electronics Z80 Z80 computer

This computer needs a name - I'd welcome any suggestions! I have built a circuit on another piece of stripboard that will handle memory, clock signal generation and the Z80 itself. A few posts ago I was wondering about how I'd partition memory. To date I've been using a very simple circuit where the lower 32KB of addressable memory is mapped to ROM and the upper 32KB is mapped to RAM. As my ROM chip is 128KB and I have two 32KB RAM chips, this seems a bit wasteful. The memory layout I'm now using is quite simple: the upper 32KB is still mapped to RAM.

Comments BBC BASIC Electronics Z80 Z80 computer

LCD Timing
Last time I discussed the hardware I mentioned I had LCD timing issues. I have finally resolved them, but this has been the most time consuming part of the project so far. The first thing to sort out was the LCD's E pin. Once you have set up the LCD's input pins to a state where they're ready to read or write data, you need to drive this pin high. I had had some success by holding it high permanently and relying on the Z80 to set all the other to the right state at roughly the same moment, but this was inaccurate and resulted in occasional display glitching.

Comments Electronics Emerson LCD PG12864LRS Z80 Z80 computer

A computer needs some way of interacting with the outside world via input and output devices. It's about time, then, that the Z80 computer project acquires a section dedicated to I/O. The Z80 differentiates between memory and I/O devices, though both share the data bus and the address bus. You can control I/O devices using the in (input) and out (output) instructions. When you input or output you must specify a device address and a value or target register. For example,
in a,($20) ; Read a value from device $20 and store it in A.

Comments Electronics LCD PG12864LRS Z80 Z80 computer

Now armed with a flash programmer, I thought it about time to try and build a Z80-based system. Click for video (829KB WMV) Not much to look at, and it doesn't do much either. The large IC in the bottom-left, prominently marked Z, is the Z80 itself. To its left is a 555, generating a ~220Hz clock signal (yes, Hz, not MHz or even kHz). Above the Z80 is another large chip - this is the 128KB flash ROM. The eight parallel wires between them are the address bus - only A0 to A7 are connected. This only lets the Z80 address 256 bytes, but that should be enough for testing.

Comments Electronics Z80 Z80 computer

I've decided to switch to a regular 10MHz Z80 rather than a Z180, given the difficulty of using an SDIP 64. I now have a DIP 40 Z80 ready for use, but as I don't have the programmer for the Flash chip (which will hold the OS) there's not much I can do with it physically. I have therefore cobbled together a basic emulator to help develop some of the software beforehand. To cut hardware costs I'm going to try and handle input in software. One bit of hardware I'm planning on having is an eight-bit open collector I/O port.

Comments Electronics Emulation PICAXE PICAXE-28X1 Z80 Z80 computer

I gave in and rewrote all of the Z80's interrupt emulation from scratch, finding some rather horrible bugs in the existing implementation as I went. Some of the highlights included non-maskable interrupts ignoring the state of the IFF1 flag (this flag is automatically cleared when an interrupt is serviced, and is used to prevent the interrupt handler from being called again before it has finished) and the RETN instruction not copying the state of the IFF2 flag back to IFF1. When non-maskable interrupts are serviced, the state of IFF1 is copied to IFF2 before it gets cleared, the idea being that if you use RETN interrupts are automatically re-enabled on exit of the NMI ISR.

Comments Cogwheel Sega Sega Master System Z80

After seeing Scet and Drilian's work on their respective emulator projects I decided I needed to do something with the stagnating Cogwheel source on my hard disk drive. The only ROM I have tested where I can't find an explanation for a bug is the Game Gear Garfield: Caught in the Act game. Like many games, when left at the title screen it'll run a demo loop of the game in action. At one point Garfield would walk to the left of the screen, jump over a totem pole, shunt it to the right and use it as a way to jump out of a pit.

Comments Cogwheel Emulation Sega Sega Master System Z80

My work with the VDP in the Sega Master System made me more aware of how video signals are generated, so thought it would be an interesting exercise to try and generate them in software. This also gives me a chance to test Brass 3, by actively developing experimental programs. I'm using a simple 2-bit DAC based on a voltage divider, using the values listed here. This way I can generate 0V (sync), ~0.3V (black), ~0.6V (grey) and 1V (white). My first test was to output a horizontal sync pulse followed by black, grey, then white, counting clock cycles (based on a 6MHz CPU clock).

Comments Electronics PAL TV Z80

Brass 3 Website. I've released a beta version of the new assembler. It comes with the compiler, a GUI builder (see the above screenshot) and the help viewer; it also comes bundled with a number of plugins. I've also knocked together a quick demo project that can be built directly from Explorer once Brass is installed. There are a number of missing features (such as a project editor, project templates and multiple build configurations) and no doubt broken, incomplete or untested components - but at least it's out in the wild now, which gives me an incentive to fix it!

Comments Brass Z80

OS 1.15 appears to boot, and if I run an OS in Pindur TI, archive the files (copy them to Flash ROM) then use that ROM dump in my emulator the files are still there, where they can be copied to RAM. Trying to re-archive them results in a fairly un-helpful message, as I haven't implemented any Flash ROM emulation (nor can I find any information on it)... Applications (which are only ever stored and executed on Flash ROM) work well, though. I've also updated the LCD emulation a little to simulate the LCD delay; greyscale programs (that flicker pixels on and off) work pretty well now.

Comments Emulation Stetson TI-83+ Z80

Brass 3 development continues; the latest documentation (automatically generated from plugins marked with attributes via reflection) is here. The compiler is becoming increasibly powerful - and labels can now directly store string values, resulting in things like an eval() function for powerful macros (see also clearpage for an example where a single function is passed two strings of assembly source and it uses the smallest one when compiled). Thanks to a series of hints posted by CoBB and Jim e I rewrote my TI-83+ emulator (using the SMS emulator's Z80 library) and it now boots and runs pretty well.

Comments Brass Emulation Stetson TI-83+ Z80

Quake isn't dead, but I've shifted my concentration to trying to get Brass 3 (the assembler project) out. Brass 2 didn't really work, but I've taken a lot of its ideas - namely the plugin system - and kept some of the simplicity from Brass 1. The result works, and is easy to extend and maintain. Last night I got it to compile all of the programs I used for testing Brass 1 against TASM successfully. I'm taking advantage of .NET's excellent reflection capabilities; one such example is marking plugin functions with attributes for documentation purposes, meaning that all you need to get Brass documentation is to drop your plugin collection assemblies (DLLs) into the Brass directory then open the help viewer app.

Comments Brass C# Z80

All of this Quake and XNA 3D stuff has given me a few ideas for calculator (TI-83) 3D. One of my problems with calculator 3D apps is that I have never managed to even get a raycaster working. Raycasters aren't exactly very tricky things to write. So, to help me, I wrote a raycaster in C#, limiting myself to the constraints of the calculator engine - 96×64 display, 256 whole angles in a full revolution, 16×16 map, that sort of thing. This was easy as I had floating-point maths to fall back on. With that done, I went and ripped out all of the floating-point code and replaced it with fixed-point integer arithmetic; I'm using 16-bit values, 8 bits for the whole part and 8 bits for the fractional part.

Comments Quake Raycasting TI-83+ XNA XNA Quake Z80

This post got me wondering about a TI emulator. I'd rather finish the SMS one first, but so as to provide some pictures for this journal I wrote a T6A04 emulator (to you and me, that's the LCD display driver chip in the TI-82/83 series calculators). In all, it's less than a hundred lines of code. The problem with TI emulation is that one needs to emulate the TIOS to be able to do anything meaningful. Alas, I had zero documentation on the memory layout of the TI calculators, and couldn't really shoe-horn the ROM dump into a 64KB RAM, so left it out entirely.

Comments Brass Emulation Game Gear Stetson TI-83+ Z80

No updates for a while, I'm afraid - things have been pretty hectic. I packaged up and released the Sega Tween demo I'd been working on. As you can see, I added an SMS and a 3D mode - this works with the SMS 3D glasses. The extra 3D is quite cheap to calculate - shift the rotated X coordinates one way for one eye, then the other way for the other eye. After projection to the screen they need to be shifted back a little way to re-centre, but it works quite well. However, I had neglected the fact that the SMS1 (which has the card slot, and hence the model that supports the 3D glasses) had a bug in the VDP and as such only supports four zoomed sprites per scanline.

Comments Brass Sega Stereoscopy Z80

The VDP can generate two different types of CPU interrupt. The first, and easiest, is the frame interrupt, which is requested when an entire frame has been generated. This is requested, therefore, at a regular 60Hz in NTSC regions and 50Hz in PAL regions - it's a useful timer to synchronise your game to. The second, and more complex, is the line interrupt. This interrupt is requested when a user-definable number of scanlines have been displayed. An internal counter is decremented each active line (and one more just after), and when it overflows it resets to the value held in a VDP register and requests the interrupt (so 0 would request an interrupt every line, 1 every other line and so on).

Comments Cogwheel Emulation Sega Z80

One chap I cannot thank enough is CoBB for all his hard work in the Z80 field. I've rewritten the Z80 emulation from scratch; this time it uses an expanded switch block (the 'manual' way) to decode instructions. Rather than write every combination of instructions out by hand, the code making up the switch blocks up is generated by another program, reading instruction information from a table copied from an Excel spreadsheet. At the cost of a significantly larger assembly (from 40KB to 140KB) I now get a 100% speed increase (from ~50MHz to 100MHz).

Comments Cogwheel Emulation Sega Z80

I've added better memory emulation (that is, handling ROM paging, RAM mirroring and enabling a BIOS or not). I wouldn't dare say "more accurate", as that might indicate that something about it is partially accurate. I've isolated one of the biggest problems - and that's programs getting caught in a loop waiting for an interrupt that is never triggered. The source of these interrupts is the VDP. It can generate two kinds of interrupt - on a line basis (where you can configure it to fire an interrupt every X scanlines) or on a frame basis (where it fires an interrupt at the end of the active display).

Comments Cogwheel Emulation Sega Z80

The Z80 core is now a bit more accurate - ZEXALL still reports a lot of glitches, and this is even a specially modified version of ZEXALL that masks out the two undocumented flags. The VDP (Video Display Processor - the graphics hardware) has been given an overhaul and is now slightly more accurate. A lot more software runs now. I have also hacked in my PSG emulator (that's the sound chip) from my VGM player. It's not timed correctly (as nothing is!) but it's good enough for testing. Picohertz, the demo I have been working on (on and off) now runs correctly.

Comments Cogwheel Emulation Sega Z80

I'm not really clued up on the way these new-fangled modern operating systems handle running multiple threads, so I apologise in advance if this isn't really proper multithreading. Basically, I was pondering (as one does) whether it would be possible to run any number of threads on the TI-83 Plus. I daresay others have done this in the past, but not having access to the internet at the time to check I thought I'd do my own bit of experimentation. The way I can see this working is to give each thread a small amount of time to run in (time slice).

Comments TI-83+ Z80

When developing an assembly program, you need to 'declare variables' by attaching an address (in RAM) to a label. The problem here, of course, is having to calculate all the relevant positions in RAM for each variable. For example,
ram = $C000 ; Assume RAM starts at address $C000 var1 = ram+0 var2 = ram+1 var3 = ram+3 ; var2 is 2 bytes! ; ... and so on ... Now this is fairly painful. So, I added .varloc and .var directives to Brass:
ram = $C000 ; Assume RAM starts at address $C000 .varloc ram, 1024 ; 1024B in size .var 1, var1 .var 2, var2 .var 1, var3 ; ...

Comments Brass Z80

Reliability
I'm sure you wouldn't want to use a keyboard that was inaccurate. Unfortunately, (as you might have seen me moaning in the past) the keyboard generates the clock signal. This basically means you need to be constantly checking the clock line to see if it goes low - that or use a hardware interrupt the jumps in and receives the scancode packet when the keyboard decides you want to stop sending something. Well, I don't have the luxury of an extra keyboard chip or a hardware interrupt, so I needed to don my thinking cap.

Comments Emerson TI-83+ Z80

Once again, I waste my time doing something remarkably useless - it's trying to connect a keyboard to my TI graphing calculator! Idea
Alas, this is not an original idea - I had seen some work done on this in the past, and tried fiddling with the code myself, not really understanding much of it. I decided to have a go - from scratch, and on my own. Constructing the hardware
I decided to butcher an old, suitably discoloured keyboard (in a nice way, though, so if all went wrong I could reassemble it).

Comments Emerson TI-83+ Z80

Attack patterns can now be simply scripted as a list of 4-byte chunks, covering which enemy to use, the delay between adding them, how many of them to add, the delay between them and a delay after adding the last one. For example, this:
.db $04,16,8,100
...would add 8 enemies of type $04, adding one every 16 game ticks and then pausing for 100 game ticks after adding the last one then progressing to the next scripted enemy. To support this, I've added some new per-level parameters, covering:
Attack type (random or 'scripted') with delay between enemies or a pointer to script to follow.Speed of enemies.Speed of landscape scrolling (used very little - bonus levels with no enemies/mines scroll past extra-quickly).Maximum number of mines.

Comments Fire Track Game Gear Z80

Fire Track II for TI-83 Plus: 31 source files. Fire Track for the Sega Game Gear: 42 source files. Based on this information alone, you can deduce that FTGG will be vastly superior. I just gave FT2 a try in VTI (I don't have any batteries in my calculator) and good grief it's slow. FTGG is much much faster... (though you should see it go when I set the enemy speed to two... I need more accurate control of speed, 1 being medium-ish easy, 2 being nightmarishly impossible!)
This makes me happy. Things to notice about the above screenshot:
Near pixel-perfect parallax star background (you can see some through the bullet holes!)Not one single poorly timed VDP write.

Comments Fire Track Game Gear Z80

Latest video. [2.29MB AVI]
You chaps probably don't know what a major headache it is trying to get clear, non-wobbly video... I gave up in the end and went for the "propped-up against a wall with camera on stack of books" approach. The reason I cannot, therefore, appear to play the game very well is because I cannot see the screen. All I can see is a faint, inverted glow and have to guess where I am. Not fun. Here are the major updates since last time:
Removed Blackadder theme Altered colour contrast on title screen, added wipe to clear it in imitation of original, restructured code for better fades, changed timing, added sound.

Comments Fire Track Game Gear Latenite TI-83+ Z80

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