Interfacing with TTL logic

[Joel Moore]

I was hoping someone here could help me figure out what I need for a circuit to connect a TriPLC to TTL I/O.  Specifically, the PLC's inputs.  I understand we need transistors but I was hoping for something a little more detailed.

I see the T100 Manual has a circuit on page 1-4 detailing something similar for CMOS.  Is this all we need?  I was under the impression that CMOS and TTL are not compatible so I was hesitant to implement what is shown there.

Ideally there would be a DIN-rail  mountable module I could use but either these aren't common for some reason or else I'm searching on the wrong terms.  The few I've found tend to be very expensive -- more expensive than is justified by a few transistors.

[support]

Do you mean you have TTL output from some electronic circuit that you wish to connect to the PLC's NPN input? If that is the case, then the ULN2003A or ULN2803A based circuit described in the manual will work with your TTL output.

If these are simple digital I/O (not high speed encounter signal, etc) you can also use the EXP4040 which provides 16 CMOS level input. There shouldn't be any problem interfacing these CMOS level inputs to the TTL signal outputs from circuit board.

Actually unless you have a very old circuit board, the term TTL may just be a misnomer as most electronic ICs today are CMOS based. The manufacturer of the circuit board may have used the name "TTL" to describe their 5V logic level I/O.

[Joel Moore]

You're right.  It could very well be CMOS.  I'm just going by what the customer said.  And yes, it's an output that I'm trying to interface with the PLC's input and it's low speed.

I'll check out the 2003A chip.