Example: EX_EXPIO.c

Ttelmah · Joined: 11 Mar 2010 Posts: 19982

Yes. The point is that with my approach, the first byte will be the
first bit from the chain from each chip. Makes the organisation very logical.

JAM2014 · Joined: 24 Apr 2014 Posts: 143

Hi All,

A couple of things. This equipment transmits the 384 bits at 9600 baud at a maximum repetition rate of every 2 seconds. As I previously mentioned, this has been working like this for 30+ years. In recent years, we have been putting an FTDI based serial-to-USB converter chip in these instruments, and that works great, but there are a number of EOL devices in this design that prompts the new work. Trust me, the 'can has been kicked down the road' for about 2 decades already, and now it's time to act! This update will have to be done in stages as the new control circuitry has to support the old 74LS165 wiring because of repairs to existing units as well as to support current inventories of PCB's. Later, the 74LS165 chains will be simplified to eliminate the 'non-data' bits that are currently required to form a complaint RS-232 transmission.

Thanks,

Jack

temtronic · Posted: Wed Nov 12, 2025 1:52 pm

food for thought.....
Any chance you can piggyback a new,improved 'daughter' PCB onto the current ones ?
One that connects to the '165 data inputs and the RS-232 output, bypassing 'all the rest' ?
I was down a similar road 4 decades ago (prePIC), did the mother/daughter PCBs as a quick,cheap 'bandaid' that gave me time to totally redo the main board.

Whatever path you take, use the biggest PIC the the family ! My goto PIC is still the 18F46K22, 40 pins, LOTS of I/O,memory,speed 3/5 operation. Some think smaller PICs are fine( aka lower cost) , until they need 2 more I/O pins, or just 240 bytes of memory.