Articles tagged “BBC BASIC”

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

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

Work commitments have left me with little time to pursue my own projects of late, hence the lack of updates. A chap named Jeremy contacted me with problems relating to the IThumbnailProvider code I'd posted here before. We narrowed it down to a 64-bit issue, demonstrated by the fact that the thumbnails appeared in the file open dialog of a 32-bit application, but not in Explorer. Not having a 64-bit version of Windows to tinker with, I was unable to help, but he found the solution was to register the assembly using the 64-bit version of regasm.

Comments 16F84 BBC BASIC Clock Electronics IThumbnailProvider PIC TI-83+

Work on BBC BASIC has slowed down quite a bit, with only minor features being added. A *FONT command lets you output large or font sized text to the graphics cursor position regardless of the current MODE:
10 MODE 3 20 VDU 5 30 MOVE 0,255 : PRINT "Small" 40 *FONT LARGE 50 MOVE 0,227 : PRINT "Large" 60 VDU 4 70 PRINT TAB(0,3) "Small (VDU 4)" Another new command is the dangerous *GBUF that can - when used correctly - let you switch the location of the graphics buffer. You can simulate greyscale by quickly flickering between two different images on the LCD, which is where this command may come in use.

Comments BBC BASIC TI-83+

BBC BASIC may have originated with the 8-bit home computer era, but it's still being updated and its most up-to-date incarnation - BBC BASIC for Windows - has a wealth of features that are unavailable on the Z80 version. The BBC BASIC graphics API is primarily accessed via the multi-purpose PLOT statement. PLOT is followed by three arguments - the type of graphics operation being carried out followed by an X and a Y coordinate. For example, to draw a line between (20,30) and (100,120) you could do this:
PLOT 4,20,30 : REM Move graphics cursor to (20,30) PLOT 5,100,120 : REM Draw a line to (100,120) This results in needing to remember a lot of different plot codes (there is a logic to how they are formed but I still need to consult a list of codes from time to time).

Comments BBC BASIC TI-83+

Work commitments have prevented me from doing much on my own projects recently, but zipping up a few files to get BBC BASIC tested is not a time-consuming process so I've started to release test builds. Download latest version The documentation is available online. It's generated by a little tool I hacked together to turn a MediaWiki database into a CHM file. I've had a few issues with the TI-84+ hardware, such as LCD corruption, difficulty in getting key presses to register and crashes when USB devices are unplugged.

Comments BBC BASIC TI-83+

I hope you all had a good Christmas and New Year period! I received an Xbox 360 controller for Christmas, so have done a bit of work on Cogwheel to add support for it. (You can download a copy of the latest version 1.0.2.0 with SlimDX here). The first issue to deal with was the D-pad on the Xbox 360 controller. When treated as a conventional joystick or DirectInput device the D-pad state is returned via the point-of-view (POV) hat. The joystick input source class couldn't raise events generated by the POV hat so support for that had to be added.

Comments BBC BASIC C# Cogwheel Sega Sega Master System TI-83+

The BBC Micro had a virtual resolution of 1280×1024, meaning that if you drew a circle centred on (1280/2,1024/2) it would appear in the middle of the screen regardless of its pixel resolution. On top of that, (0,0) was in the bottom-left hand corner of the screen with the Y axis pointing upwards. Thus far I'd been using the slightly more intuitive fixed resolution of 96×64 with (0,0) in the top-left hand corner with the Y axis pointing downwards. This means that any graphics program for the TI-83+ version appears upside down and squashed into the bottom-left corner when run on the BBC Micro.

Comments BBC BASIC TI-83+

Work on the TI-83+/TI-84+ port of BBC BASIC continues bit-by-bit. Source code of TRIANGLE demo on the left. I've added triangle filling (left) and, by extension, parallelogram filling (right) PLOT commands. The triangle filler is a little sluggish, tracing each edge of the triangle using 16-bit arithmetic, but it seems fairly robust. I am trying to focus on robustness over speed for the moment, but it would seem easy enough to add a special-case triangle edge tracer if both ends of the edge can fit into 8-bit coordinates (all inputs to plot commands use 16-bit coordinates).

Comments BBC BASIC TI-83+

Progress on the TI-83+/TI-84+ port of BBC BASIC continues - I'm hoping to get a beta release out soon. I've done quite a lot of work on the graphics features. Every shape that is plotted can be set to either the foreground colour, background colour or to invert the pixels it covers. This wasn't implemented properly (everything was always drawn in the foreground colour) which has been corrected. The first image in the above group shows the flood-filler in action, filling inside and outside a triangle.

Comments BBC BASIC TI-83+

It's been a while since I worked on the TI-83+ calculator port of BBC BASIC, and due to a relatively modular design some of the new features I'd been working on for the Z80 computer project version could be easily transferred across. The first addition to the calculator port is the TIME$ keyword, which lets you get or set the system time. That's all very well and good, but only the TI-84+ calculator has real-time clock hardware - the TI-83+ doesn't have any sort of accurate timekeeping to speak of.

Comments BBC BASIC TI-83+

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

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

I've got a fairly hackish "graphical text" mode set up (enabled with VDU 5, disabled with VDU 4) that causes all text that is sent to the console to be drawn using the current graphics mode (at the graphics cursor position, using the graphics colour and logical plotting mode and graphics viewport). This allows text to be drawn at any position on-screen, but is (understandably) a bit slower and doesn't let you do some of the things you may be used to (such as scrolling text, copy-key editing and the like).

Comments BBC BASIC TI-83+

Back to work on the TI-83 Plus port of BBC BASIC! To complement the graphics viewport I've added support for text viewports — this lets you define the area the text console uses. The following VDU commands are now supported:
VDU 24,<left>;<top>;<right>;<bottom>;
Define a graphics viewport.VDU 28,<left>,<top>,<right>,<bottom>
Define a text viewport. VDU 26
Reset both viewports to their default settings (full screen). VDU 29,<x>;<y>;
Defines the graphics origin. The above screenshots defines the graphics viewport to fill the left hand side of the screen and shunts the text viewport over to the right half, using the following code:VDU 24,0;0;47;63; VDU 28,12,0,23,9 VDU 29,24;32;I've also added simple sprite drawing to BBC BASIC's PLOT command.

Comments BBC BASIC Spinning cube TI-83+

qarnos — author of the superb Aether 3D engine — has been lending a hand with the BBC BASIC graphics API and contributed a large amount of very useful code. First up is some code to clip 16-bit line coordinates down to 8-bit coordinates. This allows for lines to be partially (or completely) off the screen. He's also written a fast ellipse drawing and filling routine. The ellipses are also clipped to the viewport and are filled with an 8×8 pixel pattern. The graphics viewport can be redefined using the VDU 24,left;top;right;bottom; command as demonstrated in the above example.

Comments BBC BASIC Spinning cube TI-83+

Work has been keeping me busy recently, but I've tried to set aside a small amount of time each evening to reclaim some sanity and do a little work on BBC BASIC. Not much progress has been made, but there has been some at least. On the left is the program running on an 83+ SE at 15MHz, on the right on the regular 83+ at 6MHz. If you really wanted to do 3D in BBC BASIC you could probably get away with writing some of the more expensive operations — such as transforming/projecting vertices in batches — in assembly, but that would sort of go against the whole point of trying to write a program to test the speed of BASIC.

Comments BBC BASIC Spinning cube TI-83+

Richard Russell has kindly supplied the project with the BBC BASIC relocatable modules — compiled object files which can be relocated to any memory address by a linker — which means that BBC BASIC can now be configured to run on the TI's hardware. The tools to relocate the modules run under CP/M, which means that rather trying to integrate the relocation into the build process (which would be a little awkward) I'm going to relocate the modules to a fixed base address and inject the resulting binary file directly into the application.

Comments BBC BASIC TI-83+

I've started working with the actual BBC BASIC interpreter. As it won't run in its current state on the TI calculator (it relies on a jump table at &FF80..&FFFF to interact with the host, which is protected) I'm using the Z80 emulator I wrote for Cogwheel to try and puzzle out what the host interface should be doing from the relative sanity of C# code (the jump table is populated with OUT (n), A instructions which are subsequently trapped and handled by the emulator). One thing I hadn't realised is that the graphics operations that BBC BASIC offers are actually implemented via the OSWRCH handler (OS WRite CHaracter), which means that BBC BASIC's PLOT, MOVE and DRAW commands will also be available, as well as any commands that use them indirectly (such as CIRCLE).

Comments BBC BASIC Emulation

This is a project I initially attempted to get off the ground about four years ago, but never did. Anyhow, I've started work on it, and thanks to help from Richard Russell (the original developer) and J.G.Harston (who comparatively recently developed the Sinclair ZX Spectrum port) it looks like it should be possible this time around. BBC BASIC was the native programming language on Acorn's BBC Micro. It's a structured BASIC dialect and supports procedures and functions, permitting far nicer code than the line-numbered GOTO and GOSUB code on other contemporary machines.

Comments BBC BASIC TI-83+

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