Mini-80188
What is it?
The Mini-80188 is a very small computer with as main components an Intel 80188 CPU, 1024 KB of SRAM, 128 KB of FlashRAM and one 8-bits ISA slot for expansion. The idea is based on the Mini-V20 and 6502 -> 80188.State: Schematics, board and PCB. No BIOS.
The 80188 computer
The computer part is made out of only a few ICs:
- the 80188 CPU, IC13
- 1 MB of RAM, using two 512*8 SRAM ICs, IC16 and IC18,
- 128 KB of ROM, using a 29F010 EEPROM, IC17,
- two 573 latches for creating various address and data signals, IC14 and IC15,
- A GAL that controls everything, IC19,
- an ISA slot to be able to expand this little machine.
You probably also noticed the 74 D-fliflop, IC16, and two LEDs. It is not an essential part of the computer; I just needed something that could help me to debug things.
1 MB of RAM and 128 KB of ROM is more than the 80188 can control and that's where the GAL comes in. The 80188 has some features on board to control RAM directly but to make a long story short: they are unusable the moment you want to handle more than 512 KB. Note: that's for the older 80188s. The improved 80188EB is able to handle more memory in very neat way but a) I only have the older ones and b) I cannot solder these EB types.
So I let the GAL handles the memory management. The advantage of the GAL is that I'm completely free to chose how much ROM I need and where to place the 64 KB range for the 6502. For the moment my choice is:
- 832 KB of RAM in the 0xxxx to 0Dxxxx range
- 64 KB for the 6502 in the 0Dxxxx range
- 128 KB of ROM in the 0Fxxxx range
Remark: normally I create "an IC only" version of a schematic where normal ICs/gates are used instead of a GAL. In this case I considered the way the GAL works so obvious that I skipped it.
Debugging
I wanted a simple mean to check the working this board and the idea rose to add four LEDs, resistors and two 74LS74 D-flipflops. The 80188 had seven programmable I/O lines. Four of these lines, PCS0..3, can be programmed to act in the, AFAIK, unused range range 0140..3h. Each of the pins can negate one of the CLR or PRE input pins and turn on/off LED1/LED2 or LED3/LED4.The serial interface
The original design had no I/O at all but then I decided to add a serial interface of its own. I chose for the 16450 UART for the simple reason that I have them alying around. The idea is to connect it to a USB/RS232 interface and then I don't need +12/-12 Volt conversion.PCS4 is used to handle the UART.
The GAL
The GAL has tree functions:-
The ISA bus needs the signals MEMR, MEMW, IORD and IOWR. In a PC/XT the Intel 8288 generates these signals using the signals S0, S1 and S2 as input. In this case the GAL generates the signals.
- Using the address lines A16..23 plus MEMR and MEMW as input, the GAL generates the enable signals for the two RAMs and the ROM.
- The GAL inverts the two ISA signals IOCHRDY and IOCHCK because these are active (L) and the 80188 expects an active (H) for SRDY and NMI.
The board
Software
It seems there doesn't exist any software for this card. Or does it? I recreated the 8088 card developed by Commodore for the CBM-II series like the CBM 720 and CBM 610. These computers have a 6809 CPU on board. This card isn't PC compatible at all and yet Michał managed to run DOS 3.3 on it without any changes to DOS itself but using a very clever BIOS. So I have hopes :)You can email me here.