PALs (was Re: MITS 2SIO serial chip?)

--- ajp166 <ajp166(a)bellatlantic.net> wrote: It depends on what your limited resource is and how costly _that_ is. ISTR PALs were $2-$10 each c. 1981-1982. If someone remembers differently, please supply more accurage data. Yes, a single PAL cost more than several TTL popcorn chips, but given how much you could fold into a single PAL in the way of I/O select logic (a common use on the board I first encountered PALs on), it wasn't so expensive then. Or if board space was a fixed resource, then it's doubly costly. The oldest example I can cite from personal experience is the COMBOARD-I to COMBOARD-II design. Both were early examples of 68000 designs (an intellegent Unibus serial periperal)... one with SRAM (2114s) and TTL logic, the other with DRAMs and PALs. One similarity - about 1.5 sq ft. of board space to cram in a CPU, RAM, support logic, a sync serial port (based on the COM5025) a parallel port and Unibus DMA logic. In 1981, our designers went with older tech, but the DMA engine was horribly complicated from the standpoint of the 68000, but it was in part because there wasn't enough room on the board for a better design with TTL. The second revision (c. 1983-1984) had more onboard I/O, and implemented the DMA engine as a bank of shared memory to the 68000 (i.e., read/write to a certain range of memory from your code and it automatically generates a Unibus DMA cycle - most cool). I don't know for a fact, but engine would have fit on a Unibus board if it had been made out of popcorn logic. I didn't see PALs in use until the early 1980s. Yes, I know they came out in 1978, but products designed with them didn't hit right away. The technology is 1970s, but the products are, for the most part, 1980s. -ethan __________________________________________________ Do You Yahoo!? Send your FREE holiday greetings online! http://greetings.yahoo.com