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IBM PC 8088 changed with a Motorola 68000 – MicroCore Labs

IBM PC 8088 changed with a Motorola 68000 – MicroCore Labs

2023-05-12 08:25:54

I used to be questioning what the IBM Private Pc would have been like if they’d chosen the Motorola 68000 as an alternative of the Intel 8088, so I used my MCL86+ to emulate the 68000 and discover out!

The MCL86+ is a board which makes use of a Teensy 4.1 to emulate a microprocessor in C code in addition to use its GPIOs to emulate the native bus of the Intel 8088. It may be used as a drop-in alternative for the Intel 8088 and could be cycle correct in addition to run in accelerated modes.

For this venture I swapped the 8088 emulation code with my MCL68 code which emulates the Motorola 68000. The 8088 native bus emulation was stored in order that all the 68000’s reminiscence reads and writes may move by means of to the IBM motherboard.

Emulating the 68000 is okay, however not very helpful with out an working system or another software to run on it. I selected to make use of Gordon Brandley’s 68K BASIC which was revealed in Dr. Dobbs Journal again in 1985.

I ought to word that simply the 68000 emulation is working within the MCL86+. The entire IBM motherboard peripherals, video, and reminiscence are used for this venture. Video is drawn to the IBM MDA card’s video reminiscence over the ISA bus. BASIC is run out of 64 KB of the motherboard DRAM which is refreshed by the 8327 DMA controller by an interval set by the 8253. The keyboard receives the serial knowledge and generates an interrupt by means of the 8259 and is cleared by accesses to the 8255. Mainly all the main parts and glue logic of the IBM motherboard are used!

I ran a couple of exams and it appears that there’s not a lot of a efficiency distinction between working an 8088 and a 68000 on the IBM motherboard which makes use of 8-bit chips completely. If IBM had chosen the 68000 they might even have used the 68008 which is a 68000 with an 8-bit native bus interface. Maybe this chip was not accessible on the time IBM’s venture, code-named ‘Chess’, was in growth. It may even have been the case that Microsoft didn’t have an working system or BASIC ported to the Motorola 68000 structure. What this venture exhibits is that the efficiency distinction was not so profound that it will have made a distinction in IBM’s choice course of.

Listed here are some movies of the machine in motion:

I hope this venture helped fulfill those that have puzzled what the IBM Private Pc would have been like if they’d chosen the Motorola 68000 as an alternative of the Intel 8088!

IBM PC 8088 replaced with a Motorola 68000

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