TTL serial receiver, no PIC, UART or software- just pure primitive logic please

ds18s20

Hi

I am trying to figure a way to build a totally primitive rs232 receiver (ttl levels), the objective is really to shift 8 bits and then validate them so that they are latched by the next IC which will be a simple 8 bit latch. You might say sure, easy but I always find potential problems with my design. yah sure I figured an 8 bit shift register, decade counter and some glue logic. But that kind of contraption can get totally out of sync and stay that way pretty much forever. If anyone have had that idea before and came up with better design please do share. What is the magic sync design

~B

Paul Baker

This is usually accomplished via a state machine. Midway through EEL3112 we designed a serial UART using a 22V10. I don't think I still have the material but Ill check. In principle you capture the pulse width of the start bit, wait half·a pulse width, sample wait an additional·pulse width, sample etc. More robust designs multisample arround the center (typically 3 or 5 samples) then perform majority rule to determine the value.

To do the more simple design, you would need a counter, a register, a shift register and additional glue logic.

Post Edited (Paul Baker) : 4/16/2005 4:15:10 AM GMT