I am looking into designing a data converter that must provide data from a Scale (usually referred to as an indicator) to a very old PLC that only accepts data in BCD.
The current device that does this is failing and is no longer available (for quite some time now).
BCD isn't the problem, but rather the current device outputs the BCD in TTL to a 50 pin connector. The 50 pins include 6 digits worth of BCD digits along with a Gate signal for each digit and three inputs to the BCD source. (see inputs on pins 37, 39, and 50).
Schematics are of course not available of the current device while those for PLC inputs can be found, but only 'examples'.
Question: Does anyone have experience with a PLC "and" BCD inputs such that you can tell me that the BCD data is "loaded" when one of the inputs to the source of the BCD data (pins 37, 39, or 50) is asserted?
Elaborating on the question: The BCD data is presented in a parallel fashion via the 50 pin connector. I do not have physical access to the current (failing) hardware. (it is 450 miles away. If I did I wouldn't be asking this question.)
In order for me to provide the data to the PLC per the 50 pin data cable I need to know if (again when dealing with BCD data) the PLC asserts one or more of the signals I mentioned (pins 37, 39, or 50) to "latch in" the data. I would imagine that (or something) is used to sync when the PLC "reads" the data in.
This is going to be an "old timers" type of question, this system was installed in 1981.