Arteche smART P500, Instruction Manual

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5BTIMES
0BMODBUS RTU PROTOCOL
5.5. TIMES
Package synchronization on the MODBUS protocol is maintained using time restrictions.
When a device receives a message it calculates the time elapsed between the receptions
of two consecutive characters. If the transmission time equivalent to 3.5 characters is
elapsed without receiving any further information, the device considers that the newly
received information is complete and checks the CRC, accepting or rejecting the message
depends on the result of the CRC check.
5.6. FUNCTIONS IMPLEMENTED IN THE SMART P500
The smART P500 relay is capable of responding to the following function codes:

03: Read input registers

04: Read holding registers

05: Force single coil

07: Read exception status

08: Diagnostics

16: Preset multiple registers
5.6.1. FUNCTION CODES 03 AND 04 – READING OF VALUES
In the smART P500 implementation, the function codes 3 and 4 are interchangeable.
Both can be used to read values from the relay.
Each value has an address and its length is 16 bits (2 bytes). The most significant byte
is transmitted first. Up to 125 adjacent values can be read in one operation.
However, the expression of some values of the relay has a length of 32 bits. To obtain
such values, 2 points must be read in the same operation. If it is not so the result may
be incorrect. The 16 most significant bits (MSB) are read first (have a lower address).
The 16 least significant bits (LSB) are read last (in the higher address).