Fun with GRiD and MS-DOS 5.0 w/ SDLPT, QBASIC, and TP7!

[voidstar78]

Big thanks to @0xDEADBEEF I found that I was able to boot my GRiD system to MS-DOS 5.0 (on a 720K 3.5). I just did a DISKCOPY B: B: of my original MS-DOS 5.0 boot disk (since for some reason SYS B: didn't work, so I just used Microsoft own DISKCOPY to clone the disk). Then when the GRiD system boots, mash "F" to boot from floppy disk.

Then I verified the SDDRV.SYS works when the SDLPT device is attached off the parallel port, effectively giving me a 2GB hard drive for this system (very slow access, but gives space to work with beyond a single 720KB floppy disk).

Then I verified QBASIC GORILLA.BAS example works! And I can use TPC.EXE to compile Turbo Pascal 7 PAS files (right from the SD-LPT device). The Borland Pascal 7.0 TURBO.EXE "IDE" is very slow, you can "feel" the syntax highlighting kicking in (or it's trying to cache to the file system a lot, and across LPT that's just too slow). I tried to disable all that, but their editor was still painfully slow (pretty sure this is a 4.77MHz system). So just use QBASIC.EXE editor (or EDLIN, or COPY CON if really have to), then compile with TPC from command line.

I still don't know much about the GRiD-OS stuff, but glad I can still program the system using other means.

 

[0xDEADBEEF]

have you verified whether this is a gridcase or grid compass because it looks more like a compass to me.
in that case you probably have bubble memory storage there, which is probably accessible from gridos, not sure if it can be used under dos, and if so, probably grid ms-dos 2.11 is required? not sure if newer ones (3.2 or 3.3) have support for it?

 

[Eudimorphodon]

have you verified whether this is a gridcase or grid compass because it looks more like a compass to me.

It clearly says "GRIDCASE" on the badge next to the molded GRID above the screen. A compass has a smaller, squarer screen, and I'm quite sure they won't boot a normal PC DOS floppy.

The yellow screen is interesting. GRiDCase-es with that case style came with a variety of screens, with the most common ones being your typical mediocre LCD or a red plasma display; there are references to a yellow EL model, but some of them imply it was only fitted to the government TEMPEST models?

 

[0xDEADBEEF]

I am not sure if GRiDcases had GPIB though, and it looks like EL screen and has lower res than 640x200 CGA, from photos it looks like Compass II 1139 had such screen.
On the other hand the back does not look like Compass photos I can find.
and Compass can boot DOS just fine, they are DOS compatible (but not fully IBM PC compatible).
Certainly it is unusual.


Hmm the back looks like the one described as "tempested system" here https://staff.salisbury.edu/~rafantini/grid_1550_and_1530.htm
You have got to open it up and take some photos ;-)

 

[Eudimorphodon]

and it looks like EL screen and has lower res than 640x200 CGA, from photos it looks like Compass II 1139 had such screen.

It looks like CGA resolution to me? The specs online say the Compass II with the "wide screens" had a 512x256 panel, which would actually be higher resolution vertically. Are there more pictures of this unit in other threads, because all we can see in this one is a closeup of the screen that has a "GRIDCASE" badge over it.

 

[Eudimorphodon]

and Compass can boot DOS just fine, they are DOS compatible (but not fully IBM PC compatible).

There are plenty of "MS-DOS" compatible computers out there that run "DOS" but can't boot an IBM PC compatible version of it. (Short list: Sanyo MBC-550, Tandy 2000, TI Professional, Zenith Z-100, HP-150, Apricot PC, DEC Rainbow... I could go on if you give me a minute.) Is a Compass really compatible enough to boot an IBM or Compatible's MS-DOS disk?

Also, again on the resolution thing: he's running GORILLAS.BAS, the demo BASIC game included with MSDOS 5.0's QBASIC interpreter. To run that game you're going to have to have CGA, EGA, or VGA compatible graphics, unless there's secret undocumented support for GRiD Compass video modes buries in qbasic... which seems unlikely to me considering it didn't even support Hercules.

 

[JDat]

To my knowledge, Compass can boot customized MS DOS 2.11 specially for GRiD Compass. No other MS DOS versions for Compass found so far.

 

[voidstar78]

This is a later model GRiDCASE 4 (basically a Compass II without bubble memory and no 5-pin DIN at the back). Pardon, this was a follow up to the video here. Got a bit excited to learn it could boot to regular MS-DOS 5 FDISK showed no fixed disk, so not sure if it actually has a hard drive or not (but not surprised, surely it would be of some non-FAT partition type and all that). Will be awhile before I ever open it. Heavy unit, might be a tempest model, not sure yet. And silent as far as I could tell, not even sure if the PSU has a fan. Ideal for submarines ^.^

Exciting to me because the Sharp PC-5000 (which does have bubble memory), I couldn't get it to boot using anything other than its own very specific MS-DOS 2.11 build (probably need its own proprietary drivers to talk to the LCD screen and funky disk drive controller). The Sharp manuals and ads were clear to always say MS-DOS 2.11. Plus, do these GRiD literally use an 8086 instead of an 8088? I was never sure how MS-DOS compatible that was.

 

[Eudimorphodon]

Plus, do these GRiD literally use an 8086 instead of an 8088? I was never sure how MS-DOS compatible that was.

There are some hardware gotchas you need to take into account (mostly regarding I/O port addressing) if you’re building a PC compatible around an 8086 instead of an 8088, but assuming you do that right there’s no problem. IBM themselves used the 8086 in the PS/2 model 25 and 30.

(If you were building a “generic MS-DOS” computer instead of a strict PC compatible then those gotchas I mentioned don’t matter, do whatever you want and write your BIOS appropriately.)

 

[JDat]

This is a later model GRiDCASE 4 (basically a Compass II without bubble memory and no 5-pin DIN at the back).

Well... Visually - yes, the looks similar, but...
1) Compasses don't have F* function keys.
2) Internal architecture is different.
Peripheral hardware (keyboard, bubbles, modem, GPiB) are located in D000:0000 - DFFF:0000 memory segment. While on GRiDcase (IBM PC compatible) are located in 100 - 3FF I/O address space.

Screen buffer for compass aka "videoRAM" is located in 0400:000 -
0297F - For screen 320 x 240 - 9600 bytes
043FF - For screen 512 x 256 - 16384 bytes
Right after INT table (0000:0000 - 0000:03FF)

IBM PC have BIOS data are at this address.
GRiDcase videoRAM are located A000:0000 and upwards.

IRQs are different. d8259 (PIC) is located in different I/O Address space. No d8253 (PIT) timer on board, but regular interrupts happen with ~16 kHz frequency when line is drawn on display.

Also Compass have build in "COVOX". It hides inside Modem. There is 8 bit DAC IC from Analog Devices. By writing 8 bit value to address DFE4:0002 regularly you can get some beeps and boops.

3) CCPROM is totally different from BIOS. CCPROM have multitasking and memory allocation stuff in CCPROM. API calls to CCPROM are totally different compared to BIOS. In CCPROM there is jump table for API access. On IBM PC BIOS you are usually call interrupts INT10-INT1B.

4) Bootloader is totally different and loads on different address. CCPROM - 2000:0000, 2 kBybes big; BIOS - 0000:7C00, 512 bytes big

Plus, do these GRiD literally use an 8086 instead of an 8088?

Yes, Compass have true 8086 + 8087 @ 5.00 MHz clock and true 16 bit data bus on mainboard.

Sounds like I need to make topic or write somewhere on web about Compass low level things.
Right now I am working on experiment to get Composite video out from Compass 1101 + Get working 4 bit EL display with RPi Pi Pico help. Original EL display have 1 bit data bus.

From MS-DOS (software) perspective there is no difference between 8086 and 8088 CPU. Software will not notice difference.

 

[voidstar78]

Thanks for the details - I am hoping to do something with the GPIB eventually (punch writer stuff).

GRIDTerm gave me an option for INTERNAL modem, but as far as I can tell this unit doesn't have one. And I couldn't see any in-ROM DEV tools yet. And don't have a burner to write new ROMs anyway.

 

[0xDEADBEEF]

I have pile of GRiD modems. Not very useful these days.
But what is it interesting the GRiDcase 1550SX tech ref has schematics and pinout of the modem connector, it has obviously all the lines for com port but also 5V power. So if someone knows some kicad-fu it would be possible to design a pcb with max2323 level shifter and pico or esp32 with endless possibilities (wimodem or mouse for instance).

 

[0xDEADBEEF]

Yeah I knew Compass was different, but not exactly how. I got 1520 figured out pretty well now and even have working APPROM emulation for my 1520 86Box project but it requires unmapping CGA so I went down CGA emulation rabbit hole. ;(

@voidstar78 BTW if you gridcase has a floppy it does not have HDD. the JVC HDD is quite chonky and takes space of two stacked floppies in my 3Ps. Open yours up, it is very easy (two screws under the plastic inserts in the back).