Eaton PKE-COM-RTU, Руководство пользователя

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PKE-COM-RTU Modbus RTU communication interface for PKE12/32/65 03/20 MN034005EN
2.5. Structure of the master request
2.5.1. Address
•
The address of the slave (1 to 63) to which the request goes is set via the DIP switches
at the PKE-COM-RTU. Only the PKE with this address can respond to the request.
•
Address 0 is used as a so-called Broadcast (message to all bus users) from the master.
In this mode, individual modules cannot be addressed and data cannot be output from
the slaves.
2.5.2 Function code
The function code defines the type of message.
The following actions can be performed:
2.5.3 Data
The length of the data block (Data: N x 1 Byte) depends on the function code. The
function code is made up of two hexadecimal values and has a range of 00 to FF. The
data block contains additional information for the slave that will enable the latter to
perform the operation specified by the master in the function code (this information
may specify the parameters that need to be processed, for example).
2.5.4 Cyclic redundancy check (CRC
)
Telegrams in the Modbus RTU operating mode include a cyclic redundancy check (CRC).
The CRC field is made up of two bytes that contain a binary 16-bit value. The CRC check
is always run independently of the parity check for the individual characters of the
telegram. The CRC result is appended to the frame by the master. The slave recalculates
while receiving the telegram and compares the calculated value with the actual value in
the CRC field. If both values are not identical, an error is set.
2.6 Structure of the slave response
2.6.1 Required transmission time
•
The time between receiving a request from the master and the PKE's response is at
least 3.5 characters (idle period).
•
Once the master has received a response from the PKE, it must wait for at least the
idle period before it can send a new request.
2.6.2 Normal slave response
•
If the master request contains a write register function (function code 05/06/16), the
PKE immediately returns the request as a response.
•
If the master request contains a read register function (function code 04), the PKE
sends back the read data with the slave address and the function code as a response.
Function code
[hex]
Designation Description
04 Read input registers Reading the input registers (process data, parameters and
configuration) in the slave.
05 Force single coil Writing a single bit in the slave
06/16 Write single/multiple registers Write one or more holding registers in the slave.
In the case of a general telegram (broadcast), the
corresponding holding register is written in all slaves.
The register is read back for comparison.
2.5. Structure of the master request
2 Modbus RTU