How Many parameter can be read through Modbus serial moduleCI853 from a single slave and in Total
We have one batch controller unit (BCU) of Honeywell Make (Enraf 1010CB+). One BCU is having proximately 1200 (500 input register, 500 Holding register and 200 binary data) parameters. We need to do both read and write data.
BCU is having many structure data so many places we need to read a group of registers all together in one MB read Block.
4 such devices needs to be connected in multidrop fashion to one single CI853 Module.
We have total 10 Numbers of CI853 and total 10 Numbers of BCU shall be connected to CI853 in redundant mode(application redundancy).
other CI853 module shall be connected to other serial slave in the plant.
Controller used is PM862. BCU gives data on RS485 Modbus RTU. On Modscan sog=ftware the response from BCU is faster. Communication parameters used are Baud rate is 19200, parity none, stop bit 1 and Flow control None
We are using Moxa TCC80 converter in between BCU and CI853. Currently I am checking data with a single BCU
There is a huge delay in Modbus response(7-11 seconds for data update from a single BCU).
a) How many parameters one CI853 can handle for a single slave and in total
b) what can be done for speed up the communication for faster response.
As per Modbus.Org, the limitation with respect to one reply is as below,
MODBUS PDU for serial line communication = 256 - Server address (1 byte) - CRC (2 bytes) = 253 bytes.
Hence maximum of
a) contiguous 2000 coils/discrete inputs or
b) contiguous 125 Holding/Input register can be read in single query
To speed up the communication
a) Baudrate shall be increased to maximum possible value
b) Polling interval shall be reduced as much as possible