NexGen: Hacking; Gray 2 BCD Encoder (using TTL)

RE: NexGen: Hacking; Gray 2 BCD Encoder (using TTL)

dougw — Wed, 02 Nov 2022 21:34:16 GMT

If you do the lookup in your MCU instead of an external memory there is no problem with jitter.

RE: NexGen: Hacking; Gray 2 BCD Encoder (using TTL)

dougw — Wed, 02 Nov 2022 21:29:14 GMT

In the past, I used an EPROM to do the conversion - just a simple lookup table in one chip. To do 8 bits to 8 bits you just need a 256 byte memory chip.

However Gray code is used to eliminate large errors due to single bit uncertainty, so you need to be careful to only read when the data is stable.

RE: NexGen: Hacking; Gray 2 BCD Encoder (using TTL)

shabaz — Wed, 02 Nov 2022 20:31:50 GMT

Hi Cris,

I'm not super-familiar with ways to do the conversion, however there's an ancient circuit in an ancient book (with an anachronistic name nowadays: Modern Electronic Circuits Reference Manual), that might help, it is asynchronous, but seems to work. This circuit is also on the Internet Archive so probably OK to reproduce here.

This uses three XOR gates (the SN7483 chip on the right is not used):