Master's Queries And Slave's Responses; Reads And Writes To Modbus Addresses (Functions 1, 2, 3, 4, 5, 6, 15, 16, 22, 23) - Hitachi Abb Rvt Installation Und Betriebsanleitung

12 Fetch comm. event log
15 Force multiple coils
16 Preset multiple registers
17 Report slave ID
22 Mask write 4X registers
23 Read/write 4X registers
Remark: please note that for security reasons broadcast is not supported by the RVT.
3.3.

Master's queries and Slave's responses

When a master device sends a query to a slave device it expects a normal response. One of four possible events can
occur from the master's query:
– If the slave device receives the query without a communication error, and can handle the query normally, it returns
a normal response.
– If the slave does not receive the query due to a communication error, no response is returned. The master pro-
gram will eventually process a timeout condition for the query.
– If the slave receives the query, but detects a communication error (parity or CRC), no response is returned. The
master program will eventually process a timeout condition for the query.
– If the slave receives the query without a communication error, but cannot handle it (for example, if the request is to
read a non–existent coil or register), the slave will return an exception response informing the master of the nature
of the error.
3.4.

Reads and writes to Modbus addresses (functions 1, 2, 3, 4, 5, 6, 15, 16, 22, 23)

The format of a read function (read coil status (01), read input status (02), read input registers (04), read holding reg-
isters (03)) is as follows:
QUERY
Slave address
Function
Starting data address
Quantity of points
Error check field CRC
mat of a force single coil (05) or a preset single register (06) function is as follows:
QUERY
Slave address
Function
Data address
Data value
Error check field CRC
format of a force multiple coil (15) or a preset multiple registers (16) function is as follows:
STATUS
Approved
Returns log registers of communication events
0XXXX sets the status of multiple discrete outputs
4XXXX sets the value of multiple holding registers
Device specific
4XXXX and/or write of a holding register
4XXXX reads a set of holding registers and writes a set of holding
registers in one query
RESPONSE
1 byte Slave address
1 byte Function
2 bytes Byte count
2 bytes Data values
2 bytes Error check field CRC
RESPONSE
1 byte Slave address
1 byte Function
2 bytes Data address
2 bytes Data value
2 bytes Error check field CRC
SECURITY LEVEL
Public
1 byte (echo of master's query)
1 byte (echo of master's query)
1 byte
N bytes
2 bytes
1 byte (echo of master's query)
1 byte (echo of master's query)
2 bytes
2 bytes
2 bytes
DOCUMENT ID
9AKK106713A9758
RVT CO MM UNI CATI O N
The for-
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