Internet PLC Forum

Thanks for the assistance.

Unfortunately it still seems to be no go. After playing around a bit more it appears that the 485 converter is transmitting but not receiving.

However I can measure a voltage change when I would expect the PLC to respond but the converter doesn't flash its Rx LED.

To test this I wrote some code to send a modbus command once per second from the PLC and could measure V change across RS485 but the converter is still unresponsive.

Have you had any experience with converters not being compatible? The differential voltage is 5V when measured at the converter with no PLC. When measured at the PLC it is 1 V with no converter??

Thanks.

Hi Again All,

I have an array of 3 T100 PLC's (soon to be expanded to 5) for bench testing with later install into a large RS232 network.

To save programming time I would like to use a RS485 network. I have purchased a MOXA Uport 1130 USB to RS485 converter. This has been set to Com9 and RS485 2 Wire. I have connected this to the first PLC/s RS485 port along with 120 ohm (2 x 240 in parallel) terminating resistors.

For the life of me I can't get the TRIlogi program to connect to the PLC. The server opens the port OK but I don't know how to test an RS485 network from there the IR* command obviously doesn't work as it is a network.

Is there anything else I should be doing, e.g., links on PLC, etc.

Do I need the gnd connection? The distance is only 1 m.  I currently have R+(D+) and R-(D-) connected to the + and - RS485 ports respectively. I have tried every combination of polarity and gnd connection with no success.

Any help is once again appreciated.

Thanks for the reply.

I should have added more info to the original email. We are limited to only using the RS232 port as the PLC is connected to a radio modem which is responsible for all comms.

I was intending to let the SCADA push values into memory for PLC on address 1 using MODBUS. This PLC would then recognise the new data and use the same port to send MODBUS information to PLC's on addresses 2,3.....

Is this option possible?

Hi all,

Can anyone please tell me what the value of the digital output pull up resistor of the T100MD-888 is?

Also please confirm that this is connected to the power suppy rail. I'm sure it is.

Many thanks.

Thanks for the reply.

I would prefer to avoid external circuitry if possible.

What sort of accuracy are you talking about with regards to the stepper motor?  It sounds like trial and error may be needed.

Is there no way to do this using the internal clock and for statments?

Another option I have used with PWM and PICAXE micros is changing the clock speed which therefor changes the base frequencies.  Is this possible?

Hi,

Does anyone know what the stand-by load of a T100MD888 is with no external devices attached.  I need to design a battery charging system using a solar panel.

Many thanks.