edr@sri-unix (11/18/82)
With regards to the DEC Bus Handbook, they go to great lengths to try to explain the control of bus ownership for DMA applications. This area is very obscure and they almost succeed, but not quite. They go into great detail about how to design a bus master control circuit. What they don't say is that DEC makes a custom IC that implements that very function. It is implied, since they include pin numbers and the whole bit, but they never come right out and say it. Perhaps DEC doesn't really appreciate me saying it either. I had access to the part since Tektronix does its own in house maintainence on almost all our DEC computers (and we have MANY), and our maintainence group, who are sharp and do it well, had a few in their spare parts cabinets. This part was a God-send, if implemented properly, when I had to design a DMA interface for the Unibus for a research project here. The part is a "DEC 8647" Unibus arbitration circuit. You may have to seduce your local DEC rep's husband/wife to get one, but they are available. Speaking of which, the Handbook itself was a pain to get ahold of. Either DEC doesn't like giving it out, or the field offices don't interact often enough with customers who build their own DMA hardware for the Unibus to know how to really help us. I got alot of bizarre, obscure and meaningless manuals, data and information, with alot of puzzled questions from the folks at DEC before they finally figured it out and sent me the right book. Such is the life of a hardware guru, - sigh. Good luck to all, with a little perseverance, you will succeed. Ed Reuss teklabs!edr