The PC-Box
What is it?
In short: the PC-Box is my 8088 version of the SSE SoftBox: a small Z80 computer, no drives but equipped with an IEEE interface that enabled the Commodore CBM series to run CP/M 2.2 more or less. "More or less" because the CBM only acts as a terminal because the Softbox does the actual computing.Remark: this is purely a fun project for my self in the first place!
Hardware
The PC-Box can be as small as a PC board with just one LPT and COM port that, in combination with two driver ICs, can act as an IEEE interface. The board now has to be told in one or another way how to behave like a PC-Box and the idea is to use an external ROM. The advantage of using an external ROM: it can be used on almost any PC board.How to add this external ROM? There are several possebilities:
- I own an ISA card which only purpose is to add an external ROM.
- Various network cards, PCI and ISA, enable the user to add a boot ROM. But I haven't used this method yet my self.
- I once replaced the EPROM of a VGA card with my own EPROM. Worked like a charm although the VGA card itself could not be used (FYI: I used a MGP video card in that case).
- I found various modem, SCSI and other hardware cards with an on board external ROM. These cards can be used but there is a small disadvantage of using these cards in other projects than PC-Box: the onboard hardware could get in the way. Soulution, tried and tested with an old ISA Adaptec SCSI card: cut the lines coming from the IORD and IOWR pin on the card's edge connector and connect the effected pins on the card to 5 Volt.
- My own soulution: some years ago I ran into a batch of obsolete Thunderbyte anti-virus cards. Nice little cards with one disadvantage: some data lines towards the EPROM have been swapped as a kind of copy protection. So to be able to use such a card, before programming the EPROM I first have to run a little program that swaps the data bits in the correct order.
Software - external ROM
Being developed.....Software - operating system and more
What software should be run on the PC-Box? And under what operating system? The obvious OS is MS-DOS or an equivalent, like FreeDOS. But handling disks is too much integrated inside this OS. CP/M already had the same problem, the Softbox could only be run using a special prepared floppy disk.Long before having this idea about the PC-Box, I started developing my own operating system: CBM-DOS, just for fun and to learn from it. Initially it was just meant for the PC-XT but in the mean time Michał Pleban and I developed a new 8088 card for the CBM-II and I ran into my two SSE HardBoxes that I had misplaced previous year. This lead to the idea to to turn CBM-DOS in something that could run on these platforms with just one different file for each platform. The last is not new, it is the basic concept behind CP/M.
The CBM part
The only thing needed for the CBM is a piece of software that acts as the terminal for the CBM/PC-Box combination. This is being developed as well.Testing the whole
Using "just a bare board" for testing didn't sound comfortable. So the idea is to use my Commodore PC 386SX in the first place. The only thing that will be used is the video card. It enables me to output codes on the video screen to see at what point in the code the program is running (or not).You can email me here.