AB Programming through DF1


Thread Starter

Jay Kirsch


I have several AB5-20's and SLC503's on a multidropped telco circuit. Is it possible to program these controllers from the master PC with RSLinx using DF1 protocol ?

I was told by AB that when channel 0 on the 5-20 is set to DF1 mode the unit cannot be programmed through that port any longer. Is this true ? Are the SLC's different.

Thanks in advance.

Jay Kirsch
Hello Jay,
Channel 0 of PLC 5/20 is for DF1 (or serial) communication. This is a direct access using a serial cable connected to your PC and to channel 0. There is no other way of connection (that I know of) to channel 0 except for this protocol
(point to point, slave, master system, and ASCII). The same thing with SLC 5/03. SLCs are different in a way of protocols, capacity of programs but the programming is basically the same. That's why you specify a bigger capacity of
controller if you are programming something that requires a bigger amount of IOs. You use PLCs when you require a more robust programming (the use of PIDs, analog). Use SLCs for discreet type of controls (although you can also use this
for analog devices). You can try accessing those controllers using RSLogix 5 for the PLC 5/20s and RSLogix 500 for the SLCs. You can use one RSLinx but you can not use one programming software for both. I just don't have idea if you can access both CPUs using RSLogix 5000.

It's not completely clear what your multidrop telco circuit consists of, but it sounds like you're doing individual dialup stations with the RSLinx DF1 half-duplex Master driver.

You can program PLC-5 and SLC-5/0x controllers whose DF1 ports are set for half-duplex slave. When you have a continuously polling master (like on a radiomodem network) you can even hook up RSLinx as a DF1 slave in the remote location and program other slaves because the master forwards those packets.

But with a dialup system that might be impractical, as the DF1 driver will send as many packets as RSLinx requires, then maybe hang up and try to call the next station. That would be OK if the application was data acquisition, but the DF1 driver is now going to have to go through it's dialup list before it will come back to the station you're trying to go online with, and RSLogix will timeout long before that dialing sequence can be completed.

If this is a leased-line system you'll be in better shape. Otherwise you'll have to narrow down your polling list to just the station you want to go online with when you want to go online.


Ken Roach
A-B Seattle

Eric M. Klintworth

I don't know about the PLC-5/20's, but the SLC-5/03's can indeed be programmed over a DF1 half-duplex polling master network. Slower than the seven year itch, though, since every thing passes through the polling master, but it still beats driving all over the city/county/whatever. You will have to add your PC to the master's poll list, of course. (My system was 9600 baud; I wouldn't bother trying at 1200 baud.)

Eric M. Klintworth