| ??? 07/23/09 09:37 Read: times |
#167739 - how to 8243 Responding to: ???'s previous message |
Richard Erlacher said:
It seems his "issue" is with the i8243, which is an I/O port set designed for operation with the 8048 family. Unfortunately, it uses hardware-generated signals not available on the 805x, and, if one attempts to use the 805x with it, using memory-mapped I/O, it has to be a slow one, since the 805x in general is too fast for the 8243 host port. Well, once the hardware needed to connect 8243 directly to 8051 is missing, there has to be some glue logic for MOVX-style access anyway, isn't it? Without attempting to understand all the details, I'd bet this glue can be constructed so that it also maintains the proper timing for 8243 for a moderate speed 8051 (a bog-standard 12-clocker clocked at the same or at most twice the original clock is all what might be needed anyway). Richard Erlacher said:
He could, I suppose, use a fast 805x and drive his port pins with software to emulate the 8048, but that's a big job. What is "big" in this? It's only to replace all P4-P7 access with a simple sequence of 3-4 instructions. Joop appears to have successfully achieved that already. He quotes some problems with "multiplexing", though; I would like to know what does he mean by that: maybe the "bit-banging" is a bit too slow? The code he posted there is quite suboptimal, so that could be fixed easily. Richard Erlacher said:
Now, it might be quite a bit easier to replace the i8243 with programmable logic. That would work quite readily with the 805x.
Now that would mean complete redesign of the whole product: both hardware and software. A.k.a. restart from scratch. I doubt it is justified. JW |
