Modbus 100 Records At A Time.

[osbox]

Dear Sirs

A consultation'm reading a PDU with Modbus RTU Protocol has 365 records type holding register, my problem is that when I read from register 1 to 100 is perfect but the jump to read from 1 to 101 accuses me error, the problem is in the PDU as it delivers only 100 records at a time instead of the 128 records supported by the Modbus RTU, or will co Azeotech I can say that the maximum records at a time is 100. Atte. Osbox68.

[AzeoTech]

Actually, ModbusRTU is limited to 125 registers in a single read because the RTU protocol packet is limited to 256 bytes total. You therefore should be able to read 125 records without error. What error message are you getting? My guess is that your PLC is actually returning the error to DAQFactory because it has a 100 register limitation (probably due to memory or serial buffer size).

[osbox]

Thanks for your reply, is exactly as you say, but how I can read more than 125 records? from my BCMS.

Atte.

BCMS_Azeotech.zip

[AzeoTech]

So, the device will only go up to 100? In that case, if you want to use channels, give each group of 100 channels a different Offset. So, 0-99 would be Timing 1, offset 0, 100-199 would be Timing 1, offset 0.1, etc.