EA2BQH described an adapter to use a JRC NFG-170 / NFG-230 ATU.
The description is in Spanish, and a Google translation doesn't help me much, his published HEX file for a PIC12C508A helps more.
Building the device and observing the output, it seems to have two input pins and when one is high OR the other is low, it sends a ASYNC command string at 1200Bd on its output pin. The command string is repeated every 2.5s if the input condition remains. This string appears to command the ATU to review / retune.
The 12C508A is a very old chip, still available, but in low cost form, an OTP.
I have written some code for a PIC12F510 from the ground up to do a similar thing as far as I can see, and built an adapter for testing by VK1EA.
My redesign uses different pins to the original to better cater for ISCP and to utilise weak pullup as much as feasible. IN1 is pin3 (GP4), IN2 is pin4 (GP3), TX is pin5 (GP2). IN1 OR /IN2 causes the adapter to send the configuration command. The output (TX) is open collector.
Above, a view of the adapter from chip side encapsulated in heatshrink and a patch of double sided adhesive foam to fix it in the ATU. Pin3 is wired to ground, Pin4 (IN2) is green, TX is yellow, ground is black and VDD (5V) is red. The TX pin is wired to pin 6 of the opto isolatorC next to the input terminal block TB1 on the ATU. (It may be possible to cut a track and insert the module after the opto isolator.
Above is the wiring side of the Veroboard… not much in it.
Above is the four byte command sequence captured from the adapter. The command sequence is sent upon a valid input request, but not less than 0.5s from powerup.
Above, the original command sequence repeats every 2.5s if the input condition is maintained. Now depending on EA2BQH's 2.5s auto repeat is potentially a problem as it will retrigger a tune in progress and for some longer tune processes, they never complete (ie relays rattling whilst the transmitter remains keyed).
The auto repeat has been removed for the reliability. A momentary with in IN1 or IN2 can be used to trigger a tune, there is a 2s delay before another tune may be ordered.
The version described in this article is in the zip below as jrc_510. Note the different pin usage in jrc_510.
The revised hardware design and new firmware tests ok.