bit90 cassette support in mame

[goldnchild]

Hi b3rendsh,

I just discovered your bit90 repository, it's really a great collection of information (that can't be found anywhere else!)

I hacked in cassette support into the mame driver and with a little bit (actually a lot of) of normalization in Audacity, I was able to load the demo.wav. For some reason, the initial part of it was kind of "quiet" and DC biased, running a bunch of passes on the beginning I could make it look uniform.

I also tried loading the demo program by pasting it in as text, but there were some long lines that couldn't be entered in.

Interestingly, the demo program needs a ram expansion. According to the demo itself, the base machine has 18KB memory which must be 2k of memory + 16k on the TMS. By making the 0x8000 to 0xffff space ram it gives 32K available to basic.

Anyway, if you're curious I can publish my bit90 branch, let me know.

It's able to both load and save wav files.

Also I was able to make your python scripts work with some minor modifications (mostly just adjusting the # of samples)

https://www.youtube.com/watch?v=ANJGkU3odTA

[b3rendsh]

Hi goldnchild, that's a nice video you uploaded to youtube. I've used the demo in the beginning as an example to learn how to create graphics or music on the bit90.

It was common practice in that home computer era to advertise the total memory with the 16K VDP memory included. So yes, without memory expansion you actually only have 2K of ram of which 761 bytes free for BASIC programs. The demo program originally came with an instruction how to split it up in many different parts that would fit in this small amount of memory.

I'm very interested in your tape support branch! It's a cool addition to the supported features in mame.

There was also a disk expansion card + floppy drive but I never owned one and so far haven't found a dump of it's rom or any other information about it.

[goldnchild]

Hi again,

Thanks for your reply. I'm still amazed at the information that you've collected for such a rare machine.

BTW, do you have the basic breakout game?

(I think that's the one from https://archive.org/details/home-computer-8408/page/74/mode/2up )

I was going to type it in for fun, but saw you mentioned breakout on the main page readme.

I've added natural keyboard support so you can paste basic programs in.

I put my branch up at https://github.com/goldnchild/mame/tree/bit90_cassette

If you load the demo.wav file (you would need to do some repeated normalization on the very beginning with audacity to make it more uniform), then save it out and compare, the resulting file is virtually identical to the original.

[b3rendsh]

The basic breakout game I have is called dugout, it's in the basic folder.

Thanks for sharing your branch, it's really interesting.

I have uploaded a few more wav files. The beginning always contains some noise because there's a few seconds before the actual recording starts.

[goldnchild]

Dugout, I thought that was something other than breakout. (thought it was baseball haha)

Thanks for the cassette uploads!

I fixed the loading of cassettes with initial loading bias (just increased the value threshold up to 0.3 instead of 0.1, 0.2 not enough)

Testing all of the cassette wavs that you have, now all will load.

How do you use the BLOAD files of meteoric shower and cosmic crisis, do you use a call statement after BLOAD?

I also fixed the ram/cart banking, so if you don't specify a ramsize (it defaults to 32k) it will load coleco carts. If you specify a ramsize other than 32k the cart won't load.

I noticed that the lowercase a character has a stray dot on the bottom right. Is that on a real machine too?

I took the meteoric shower wave, loaded it with BLOAD then saved it with BSAVE "METEORIC SHOWER",32768,10240 and then compared the wavs with audacity, and it's amazing how close the two are timing wise, if you line up the sync gaps the save is almost exact to the original, excepting the initial bias.

[b3rendsh]

After BLOAD use the command BYE to start the game or type "BLOAD:BYE".

Coleco rom carts will also work on a BIT90 with only 2K of ram memory! The BIT90 will start in "game" mode if a Coleco (rom) game with signature "AA 55" is detected at address 0x8000, else it will start in "basic" mode and the 16K or 32K ram expansion is enabled (write to i/o port 0x4f) and a memory test is executed to determine how much ram is available, if the ram expansion test fails it's disabled (write to i/o port 0x4e). The bye command will just warm boot the computer, since the loaded game is preserved in ram the computer will boot in "game" mode and start the game. When loading a Coleco game from tape you do need the 16K or 32K ram expansion, depending on the size of the game. Most Coleco games are 16K or less.

The game rom is very similar to the Colecovision rom but not identical and not all Coleco games work on the BIT90, I made a few patches to the rom to make it more compatible. With the BIT90 you can copy a Coleco rom to tape and load the game from tape. A tape file was much easier to copy and share at the time. I think this is one of the reasons why the cooperation between Colecovision and BIT Corporation stopped. Colecovision was very strict on licensing.

I made some changes to the rom to improve readability of the lowercase characters as well, including the a, The patch files are in the mods folder.

[goldnchild]

I would have never guessed that, I see after the manual there's a line about BYE = "Closes open files and exits basic mode".

That works great! Meteoric Shower is a pretty good game, lots of stuff flying around with the ability to fly up and down.

So if it detects a coleco cart upon bootup, it will go into colecovision mode, so is it possible to access a colecovision cart while in basic mode? (like by inserting the coleco cart while basic is running, yes bad idea electrically, could theoretically fry the system)
Or could you hold down a key while booting to bypass the coleco cart boot?

That's actually quite interesting about the carts being saved to tape.

I might just hook up a reset key next. It seems to pull the CPU reset line low according to the schematic as opposed to being part of the regular key matrix.

edit: ok, hooked up a reset key bound to pageup. Doesn't seem to change modes though.

Thanks for the tip!

[b3rendsh]

Fun fact is that Meteoric Shower was built in the rom of the Dina console by Bit Corp.

Yes, to copy a cart to tape you would start the bit90 without expansion card in basic mode, and then insert the cart while it was on and bsave the rom. I would not do that today anymore because of the electricity risks, but make a coleco adapter pcb with a switch to disable the rom at boot. Since you have now created a working cassette interface in mame it's easier to create the tape file with the emulator: boot the machine with 32k ram to basic, load the coleco rom at 0x8000 with the debugger and bsave "game",32768,16384

Oh.. the bye command first switches the banked rom from basic to coleco before rst 0.

[goldnchild]

Aha, that explains why after loading the meteoric shower, setting the pc to the cart start vector didn't work, I needed to flip the rom banking addresses by reading $80.

so after loading meteoric shower, doing a "print ib!80" then "pc=804f" then "g" will run meteoric shower

and then "print ib!88" then "pc=0" and then "g" will get you back to basic

(first stopping the execution in the debugger by pressing enter)

I've been looking at the 40 column printer rom, and it looks like it hits io addresses 10,11,12 and 13. It appears to use 5 pixel wide characters and it has some graphics characters, but it grabs the alphanumeric character data from the system rom. It also contains the bit image of the two row BIT90 + logo as well as the string "Graphic & Text PRINTER".

I think that since the characters were only 5 characters wide, maybe the graphics characters were too wide for use.

It's unclear what the addresses mean, but it only reads from $12 which must be some kind of printer status.

I added the printer rom into mame and interestingly, when you boot up it says "PRINTER: 90201" on the bootup screen, and when you type COPY ON it calls 7800, hanging up waiting for a change at io port $12. The string PRINTER: 90201 is in the rom at the very end.

COPY ON executes this code:

2A89: jr z,$2A9F
2A9F: inc hl
2AA0: push hl
2AA1: ld a,$AA
2AA3: ld hl,$7FFA << looks for a signature at 7FFA of AA
2AA6: cp (hl)
2AA7: jr nz,$2AB1
2AA9: inc hl
2AAA: cpl << looks for a signature at 7FFB of 55
2AAB: cp (hl)
2AAC: jr nz,$2AB1
2AAE: call $7800
7800: jp $7817

Looking at the mame source, the centronics printer is supposed to hit addresses 48 and 4a, but running COPY ON and COPY OFF doesn't seem to do anything as far as I can tell. wpi 48,3,rw doesn't seem to trigger at all.

Maybe the centronics printer has a rom as well.

I found a nice article on the bit90 with some pictures:

https://hessburg-de.translate.goog/bit-corporation-bit-90/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=sc

[goldnchild]

So as an experiment I added

map(0x10, 0x10).lw8([this](offs_t offset, u8 data){ for (int i=0;i<8;i++){ printf(BIT(data,i) ? "*" : "_"); }  printf("\n"); }, "write printhead");

map(0x12, 0x12).lr8([this](offs_t offset) -> u8 { m_test_printer_status ^= 0xc0; return m_test_printer_status; }, "test_return_printer_status");

to give the code something to keep it running while printing.

100 COPY ON
110 FOR I=1 TO 3000:NEXT I
120 PRINT "A"
130 GOTO 110

and I can see this pattern:

which looks like it's scanning the printing dots maximum of two at a time, overlapping to the next dot, then wrapping around.

ignoring the lowest bit, which is possibly a printhead enable.

  *
 * *
*   *
*   *
*****
*   *
*   *



[MAME]> 

_*******
__******
___*****
_*__****
_**__***
_***__**
_****_**
_*******
_*******
_*******
_**_****
_**_****
_*******
_*****_*
_*****_*
_*******
_*******
_**_****
_**_****
_*******
_*******
_******_
_******_
_*******
_**_****
_**_****
_*******
_*****_*
_*****_*
__******
___*****
_*__****
_**__***
_***__**
_****_**
_*******
********
_*******
********
_*******
_*******
********
[MAME]> 

here's a D character

****
*   *
*   *
*   *
*   *
*   *
**** 


[MAME]> 

_*******
__******
___*****
_*__****
_**__***
_***__**
_****__*
_*****__
__*****_
__******
_*******
_*******
_*******
_*******
_******_
__*****_
__******
_*******
_*******
_*******
_*******
_******_
__*****_
__******
_*******
_*******
_*******
_*******
_******_
_******_
_*_*****
_*__****
_**__***
_***__**
_****__*
_*****_*
********
_*******
********
_*******
_*******
********

[goldnchild]

Doing some more experiments, really hacky but it does make an image:

Imgur

for some reason, graphics seem to be backwards
(edit: actually it seems to not be backwards but rotated 90 degrees)
(edit: it's interesting that the PLOT commands reverse the "normal" coordinate order, Y being first and X being second)

Imgur

[b3rendsh]

The article you mentioned is very good, and was the only correct info on the web about the BIT90 for a long time. Hopefully some more background can be found from Taiwan / Chinese sites when search engines get better in finding other language content. Bit Corp. had a subsidiary in Hong Kong where Spectravideo was also located. If I remember correctly there was some exchange of ideas between these two companies. The SV-328 on which the MSX standard was based would be a good comparison from hardware perspective and in my view came with much better software.

Didn't know you can do this kind of thing with the printer in mame. I found a few more pages of the instruction manual that weren't included in the BIT90 system doc. The printer could also print in red. Unfortunately I don't have the printer anymore, only the interface card. The other centronics card (for use with an Epson RX-80) had a different rom.

[goldnchild]

I was searching on info for the BIT60, BIT90 and was reading up on the BIT79 (NES clone with basic). It's fascinating to see all of these different variations of computers. At one time I had a Coleco Adam with its "Digital Data Pack" cassette drives. They were actually pretty cool in that the cassette transport was computer controlled. It's interesting how many computers used the TMS9918 and derivatives. If you get a chance, you might try the NABU emulator in mame, and connect over the internet to the nabu.ca servers.

I'd love to see any information you have on the printer, I found the "command table" and it looks like characters 1,2,3,4,27,5 do the printer control.

7811: 01 02 03
7814: 04
7815: 1b
7816: 05

02 = print hires
05 = print lores
27 = printer off

Let's see if I can figure out what 1,3,4 do

edit: looks like CHR$(3) prints bit graphics, 240 chars maximum, LSB dot is not printed (7 pin head)
edit: looks like CHR$(4) prints reverse characters (acts as a toggle) also reverses the graphics printing

[b3rendsh]

CHR$(1) switches color. The printer had a black/red typewriter ribbon.

[goldnchild]

It seems to send a 0x50 to port 0x11 at the beginning of the line when it wants to print red, and it's for the entire line, I think it resets on the next line.

Imgur

The only picture I could find on the internet of the printer is this:

https://archive.org/details/radio_amateur_magazine/RAM_043_1984_02/page/44/mode/2up

and thanks for scanning the other pages! Awesome!

I put up my experimental code, it's really hacky but it does make an image:

https://github.com/goldnchild/mame/tree/bit90_printer