Electronics newbie here...
I'm trying to build a retrocomputer, and learn digital electronics along the way. I decided to begin with the video generation part, with a fast memory copier, independent of the main processor. I don't really want to use an FPGA, I'm trying to do it the "old" way, like this guy did.
I would like to create a breadboard circuit that copies addresses "SA".."SB" of SRAM chip 1 to addresses "DA"+ of SRAM chip 2, as fast as possible. A sort of hardware fast memcopy machine.
The SRAM chips are 12ns 32Kx8 Renesas IDT71256SA (datasheet).
SA and DA would be stored inside synchronous 4bit binary counters (4 SN74F163AN chips each, datasheet), SB would reside in a buffer (SN74F541N), and I would use an identity comparator (2 SN74F521N) between SA and SB to eventually stop the counters, and thus the copy operation.
The counters would be connected like this (I understand this is the fastest way to cascade them):
I would like to use a 32 MHz clock (I know, that's a lot for a breadboard, but I hope to handle it by using uniform short wire lengths and some .01uF decoupling capacitors on the power rails and the SRAM's Vcc and GND pins), but I don't know if that's too fast for the chips.
During the copy operation, pin CS and OE of chip 1 would be low, as well as pin WE of chip 2. I would control chip 2 writing with the CS pin.
I'm having trouble understanding the timings in the datasheets. Can anybody help me figuring out:
- The maximum update delay of the 4 cascading counters i.e. how many ns does each counter add to the total.
- How many ns pass (at most) from the clock transition low to high and a stable data (valid) coming out of chip 1.
- If the above is less than 30ns (the clock cycle), maybe I could latch it in a fast latch so that chip 2 can use it as its data-in. That way while chip 1 reads a byte, chip 2 writes the previous one, effectively copying at 32MB/sec speed.
- If that is possible, how do I make chip 2 skip only the first clock cycle?
- If that's not possible, what would you change to make it work at such speeds?