SLC503 DF1 in Half Duplex Settings

Gentlemen,

I am the "radio guy" that occasionally runs into PLC challenges as follows:
My customer/integrator has found that the radios he is installing for his customer are not compatible with DF1 in full duplex but will handle DF1 in half duplex. He is using SLC503s and is using the RS232 Com 0 port. He has turned on the half duplex option in the PLC but is not having any luck. This is a point-multipoint radio system (although at the moment he is only testing to one site) and assuming the RF path is good and the radio is set up properly and he has turned off handshaking (as the radios do not require it), what other settings in the PLC must he be aware of? (He would get on himself but he and his wife are about to go on vacation and he has been banned from the computer). I told him I'd try to get the ball rolling. He is able to see the poll (via the LEDs both on the radio and on the PLC) but the PLC does not respond. He has confirmed the address is correct, and we have not yet had the opportunity to put a protocol analyzer in line to see if the poll is being corrupted. Any insight would be appreciated!
Chuck

Hi Chuck, thanks for posting.

DF1 Half Duplex protocol has a lot of variety to it, so it would be best to post the Master and the Slave programs (*.RSS) to see if they've been set up correctly.

If your customer was originally planning on using DF1 Full Duplex, then he's probably written his program with MSG instructions being initiated by the Master controller. In that case his Master SLC-5/03 should be configured with the polling mode set as "Msg, Allow Slaves to Initiate". He may also wish to increase the default Reply Message Timeout value from 1 (x20 ms) to 5 or 10.

The MSG instruction error code sometimes provides helpful information as well.

Something you mentioned caught my eye:

He is able to see the poll (via the LEDs both on the radio and on the PLC) but the PLC does not respond.

Click to expand...

Which location is this traffic "seen"; at the Master or at the Slave ?

Can you tell us what make and model of radio modem are being used ?

Ken,

Thanks for the info, I'll pass it on. To answer your questions:
The traffic is seen at the remote site first passing out of the radio's RS232 port and into the PLC via the LEDs on both devices.

The radios are the GE-MDS SD4 radios set up to emulate the older 4710 model. They are fairly new to the market place.
Thanks,
Chuck

Looks like the MDS SD4 is truely a half duplex radio (it can only communicate in one direction only). I would first lower the baud rate down to 4800 (kinda sucks but with true half duplex slower is better). I would also put in at least a 100ms "Pre Transmit delay". I'm assuming that they are using the MDS SD4 because they need a licensed radio (no line of site) however if that is not the case they are going to have much better luck (and performance) with a 900MHz license free (like FreeWave) radio that will operate in full duplex (even with DF1 half duplex).

I found the files where I did this once, with an SLC-5/05 master connecting to 13 remotes (9 ML1000 + 4 ML1500) over MDS 9810 spread-spectrum radios. In the master, Ch. 0 Driver = DF1 Half Duplex Master, Baud = 19200, Polling Mode = Msg, Don't allow Slaves to Initiate, Ack Timeout = 50, and Pre Transmit Delay = 0. The MSG instructions were daisy-chained so that a DN or ER bit from one enabled the next, until the last one reset the whole chain. The remotes are all set to DF1 Half Duplex Slave, with a unique address in each.