PDP8 Omnibus to USB interface

On 02/26/2013 11:37 PM, John Wilson wrote: I have a proto board I built that uses two port addresses and acts like a disk but the parts are static rams (8bit wide 512k x2). One port is read/write, the other is an address (high 12 bits) and the low 7 bits are just a counter. When you set the address it clears the counter and when you read or write a word the counter advances. the collective result is 19 bits of address for the ram. The code has to insure you only read or write 128 words. Extremely simple. Its volatile but a small battery solves that. The code has no skip checks as the "disk" is far faster than the pdpd-8 and always ready to read or write. I've been meaning (time as I'm busy) to build a card that take an IDE drive or CF in 16bit mode and maps the 12 bits into a 16 bit word for data as a disk. Storage is a big pdp-8 hardware limitation, memory is often short or hard to get, IO like console serial or a simple parallel (PC parallel for printers) is another. All of these can be addressed with common modern parts. The caveat is to keep the result comparable with standard IO (serial) and disk systems (RS08 or ?) lacking that the interface simple as most PDP-8 software only allows a page maybe two for a driver (page is 128 words). I'm afraid that USB driver and protocol is big enough to eat far more than a pdp-8 page. Allison