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Can Modicon Premium plc support to poll more than 120 register per modbus io scanning request

For Modbus protocol, the maximum amount of holding registers that can be read via the '03' command is 256 bytes (128 words). 
but the max number of holding registers to read cannot be 128 because "The quantity of registers to be read, combined with all the other fileds in the expected response, must not exceed the allowable length of Modbus messages: 256 bytes." 
The Modbus/RTU response to a Function 3 request includes 
node address: 1 byte 
function code: 1 byte 
byte count: 1 byte 
register data: N registers * 2 bytes each 
CRC: 2 bytes 
Therefore, the max number of registers that can be read in a single Modbus/RTU query is 125. 

In your case if you wish to read 384 registers you have break it into 4 requests, there is no way to send 384 read register in one single request. The request handling in Premium Unity Pro via implicit (IO scanning) or explicit (via communication blocks) is efficient and each request are managed quite frequently.
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