OkiePC
Lifetime Supporting Member
I think Dan has nailed it by stating that just because it has RS-485 doesn't mean it supports Modbus. This combined with the fact that the node address shows up as alphabetic.
Make 12 devices in the Red Lion. Use drop numbers 1-12. Add one tag and copy it to each of them. Put all twelve tags on a screen. See what you get.
Swap the comms + and - wires. See if anything changes.
If the device has LEDs for the RS485 port, you may be able to tell something from them. When they are backwards, you may see only a receive LED or a send LED light up. When correct, you may see rapid blips on both of them.
Technically, 2-wire RS485 is supposed to be three wire if you counted the signal common.
1) Modbus is an option. RS-485 does not necessarily mean Modbus. It could mean 'streaming'. How do you know this specific unit talks Modbus?
4) Why do you think that the user manual that shows the pinouts for RS-485 is incorrect? Why aren't pins 3, 5, and 8 on the 8 pin DIN connector the RS-485 lines?
grumble, grumble, can't copy correctly. Should be:
starting at (4)02042 [or (4)02041 or (4)02043 when you test for a one offset addressing issue]
If it were me, I'd be polling with Modscan so I could see the additional feedback, like "no connection" or "time out".
Part#MCRH-5000SLPM-O-485-Modbus-IP66X
Modscan is an alternative master to the RedLion. You use it on its own.I downloaded Modscan but am learning how to use it and I am not sure how I can use it, going through the RedLion.
The 485(+), 485(-), and ground must all be wired to the appropriate pins and will likely require a custom cable if you do not have access to screw terminal ports on the RedLion (because the pin-outs of the 9 pin connectors are not intended for use directly connecting to a 9 pin serial port on a PC/PLC).
The ASCII unit ID and the Modbus unit ID are separate things, and the device may show an ASCII unit ID of "A" but the Modbus ID is set to 1 by default.
As for the registers that you can read or write to, you may be able to get away with leaving off the 40000 (or in this case 400000) prefix and just entering something like 2053 or 2042 (as stated by in a prevuous comment). The Alicat Modbus RTU allows for only the two function codes to be called: function 03 for reading holding registers and function 16 for writing to multiple registers.
Additional info that may prove useful: When reading/writing to Alicat Modbus registers, the PLC should be indexed as base 1 to avoid reading and writing to the improper registers. I have also seen customers have issues if the data registers that use the two 16 bit registers are not decoded properly as a 32 bit float, so I would strongly second the recommendation to verify the temperature reading that was brought up in a previous post once you get it working.
If you would like to email me directly on the matter, I can be reached at [email protected]. Please let me know either through this forum or by email if you were able to get this up and running or if you have any questions, and I will do my best to assist.
I would not leave the Red Lion connected because establishing serial comm is always a *****.
There's lots of things that can trip up serial comm. If the Red Lion is connected, you have to figure out whether it is applying bias, whether it has termination built in, ya-da, ya-da.
I'd keep it as simple as possible, Modscan master on the PC with an RS-485 connection to the slave, the purpose being to prove that the slave communicates valid data from a given register.
The PC RS-485 connection can be either a USB/232 converter to a 232/485 converter or a USB/485 converter.
Modscan has not connected because it is not connected to anything. I posted the Modscan screen shots because the OP had not used a generic Modbus master to confirm communications.In the two MODSCAN32 pics above the window implies you have not made a connection. as the "Number of polls:" indicates it has not polled yet.(?)