Recent content by NetworkMan

There is eternal confusion on the part of some suppliers with regard to RS-422 and RS-485. Some assume that anything with 2 wires is RS-485 and with 4 wires RS-422. This is plain wrong. So I'd advise to connect it, just see if it works.

The cable being limited at 1200m max, the maximum distance between two slaves (or any other 2 devices) would also be 1200 meter.

Undoubtedly SAIA has had this question before. I understand that putting 32 bits in a 16 bits Modbus register is impossible, so very likely they have a solution. I have once seen a device which, when you wanted to read 1 register, just sent you the full 32 bits back. But a normal Modbus master...

It is difficult to say what's going wrong here. Only a lot of experimenting could help to find out what's wrong (there could be multiple issues at the same time): 1) The RS232 cabling setup (RX, TX, control signals) at both sides 2) Bitrate, parity bit, # of stop bits, delay between characters...

It is on TCP port 5502, first thing I thought: it's Modbus (5000 + 502), but it isn't. The client (opening the TCP connection) sends the message as given above. It starts with a byte 0x02 (STX) and ends with a 0x0D (CR). Peculiar in these messages are the + and _. The response messages are like...

I think there is no way to know what happened with the data offered to the TCP layer, but not sent out by the Ethernet layer. A close of the connection (socket close) can of course wait until the data is sent out (and ack'ed by the server) but this could, worst-case, take a very long time if the...

I wrote my first Modbus stack beginning of the 90's on a 10 MHz AT PC. The 3.5 character timing I solved by programming the 2nd (unused) COM-port to use the double bitrate and then time it to send 7 characters. But although it now was spec-conforming, the slave's implementations I worked with...

"I know that RS485 has a limitation of 32 devices per segment That is in the original spec. Now, with modern transceiver which have less than 1 Unit Load, you can have more than 32, as long as the total load of all devices is <= 32 Unit Load. But: how do you know the loading factor of each...

“How do you measure 3.5 character times back then on a PLC” No need to do strictly 3.5. Because: there must be minimal 3.5 character times, so 4 is also good. This is easy to time on a PC.

With RS-422 four wire you can only connect 2 devices to each other. So there is never a need to set an address - you always know whom you are talking to (= the other). Now it could be that the vendor says "RS-422 four wire" but actually means: RS-485 four wire. In this case, the device being the...

Profibus FMS has never been v ery popular due to its complexity, I would not be too surprised if Applicom silently dropped support for it in more recent products. Now since FMS and DP devices cannot communicate (they just tolerate each other on the cable) the only solution would be to find...

100 meters is the maximum Ethernet cable length. But if you then place a switch, you can go for another 100 meters. There is no theoretical limit, only a practical and financial limit. You could use fiber to go longer distances more easily. Or those Ethernet-over-telephone cable converters, they...

Multiple TCP masters and servers (or a combination thereof) can run concurrently on the same PC, but they need different TCP port numbers (say 502, 503..). Within each server instance, you can do what you want with the ID's, it is up to the server software to handle this. I.e. they could...

It doesnt matter that the slaves have the same registers. The master will read the data, and then store it locally at a place at its own choosing. Masters do not use the register model for their own storage; instead they store the received data somewhere in a PLC variable, or output of a...