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5.3.2 Transmission frame
The transmission frame is as follows.
1 byte 1 byte max. 203 bytes 2 bytes
Station address FC (function code) Information Error check
(1) Station address (station number)
Station addresses 0 to 247 are selectable with a 1 byte length.
Selecting a "0" address selects all slave stations and, therefore, the message will be a broadcast
message.
(2) FC (function code)
Function codes are defined with values of 0 to 255 with a length of 1 byte, as shown below. The
shaded sections indicate codes used with FRENIC-VG. Do not use "unused" function codes. Doing
so will result in an error response being returned.
FC Description
0 to 2 Unused
3 Read function code Data size: max. 99
4 to 5 Unused
6 Write function code Data: 1
7 Unused
8 Maintenance code
9 to 15 Unused
16 Continuously write function code Data size: max. 16
17 to 127 Unused
128 to 255 Reserved for Exception Response
(3) Information
Information fields contain all information items (function code, byte count, data size, data, etc.). For
details on information fields for each message type (broadcast, query, normal response, error
response), refer to Section 5.3.2.1 "Reading function codes", Section 5.3.2.2 "Writing single
function codes", and Section 5.3.2.3 "Writing multiple function codes".
(4) Error check
Error check fields contain data 2 bytes in length for the CRC-16 check method.
Because information fields vary in length, it is necessary to calculate the frame length required to
calculate the CRC-16 code from the FC and byte count data.
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