Emulating a DF1 polling slave network

[Ken Roach 194]

I'm just posting this as a way to remember what I'm doing, and maybe as a discussion of the protocol and technology behind DF1 Half Duplex. I've been working with a customer who has a DF1 Half Duplex network with an SLC-5/05 as the Master and about 14 MicroLogix as slave nodes, with license-frequency radios in between. It's been working fine for years, and now the end customer is getting alarms on his supervisory system telling him that communications has failed to one or more of the slave nodes. While doing some experiments with timeouts and channel configuration, I found myself using a shareware (it's about $50 USD) program called Docklight, that makes a pretty good serial analyzer. It also includes a simple command/response system that allows the PC to send responses to serial input. The DF1 Half Duplex poll is very simple: It's DLE ENQ NODE BCC. In hex, DLE ENQ is 10 05, and the node number is the address of the DF1 slave. The BCC byte is the block-character-check checksum of the previous three bytes, so it's always the same for a given node number. The standard acknowledgement to a DF1 Half Duplex Poll is only two bytes: DLE ACK (in hex, 10 04). So it's pretty easy to set up Docklight to emulate the responses of multiple DF1 slave devices to a single polling master. Then we can selectively disable and enable these responses to see how the timing and retries are done by the SLC-5/05. A screenshot of my configuration, in action: Edited 22 Apr 2008 by Ken Roach

[TimWilborne 108]

Good information Ken. It is good to hear from you!

[BobLfoot 302]

Second that. Makes me wonder where are we in the Sun Spot Cycle. Any chance we're near an up peak? Just a wild thought Ken.

[JeffKiper 9]

Ken I hope everything is OK with the fiancé and the boat!!!!! It is good to hear from you.