Pixsys TD320, Руководство пользователя

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The addressees of a request (one or more Slave nodes) are
selected by the Master by their ID, thus the data that transits on
the line has a precise destination.
The Master controls the line: it doesn’t have a specific ID address
and can read or write data in words or bits with one or more Slave
devices, specifying the destination ID.
Data read or written is saved in the destination device in registers
identified by a specific ModBus address (variable from 1 to
65535). Each ModBus address can correspond to a register (word
area of memory) or a single bit of a register (particular bit of an
area of memory).
Refer to the following figure for the list of possible operations in a
ModBus communication: reading and writing of a word or bit,
single or multiple.
Main features of protocol Modbus RTU
Baud-rate Programmable
Format 8,N,1 (8 bit, no parity, 1 stop) (default)
Supported
function
BITS READING (0x01, 0x02)
WORDS READING (max 30 word) (0x03, 0x04)
SINGLE BIT WRITING (0x05)
SINGLE WORD WRITING (0x06)
MULTIPLE BITS WRITING (0x0F)
MULTIPLE WORDS WRITING (max 30 word) (0x10)
Error codes ILLEGAL FUNCTION CODE (0x01)
ILLEGAL DATA ADDRESS (0x02)
ILLEGAL DATA VALUE (0x04)
Broadcast Simultaneus writing to all connected slaves using
address 0x00 and no answer from slaves.
Polling with
unknown slave
address
Polling using address 0xFF, any connected slave can
answer
6.2.1 ModBus RTU Master
The protocol ModBus Master can be configured only for the ports
COM1 and EXP1.