6-86
Function Code
The function code specifies commands. There are three function codes, as shown below.
Data
Configure consecutive data by combining the storage register address (test code for a loopback address) and
the data the register contains. The data length changes depending on the command details.
Error Check
Errors are detected during communications using CRC-16. Perform calculations using the following method.
1. The default for CRC-16 communications is usually 0, but when using the MEMOBUS system, set the
default to 1 (i.e., set all 16 bits to 1).
2. Calculate CRC-16 using MSB as slave address LSB, and LSB as the MSB of the final data.
3. Also calculate CRC-16 for response messages from the slaves, and compare them to the CRC-16 in the
response messages.
MEMOBUS Message Example
An example of MEMOBUS command/response messages is given below.
Reading Storage Register Contents
Read the contents of the storage register only for specified quantities whose addresses are consecutive, starting
from a specified address. The contents of the storage register are separated into upper 8 bits and lower 8 bits,
and comprise the data within response messages in address order.
The following table shows message examples when reading status signals, error details, data link status, and
frequency references from the slave 2 MxC.
Function Code
(Hexadecimal)
Function
Command Message Response Message
Min.
(Bytes)
Max
(Bytes)
Min.
(Bytes)
Max
(Bytes)
03H Read storage register contents 8 8 7 37
08H Loopback test 8 8 8 8
10H Write multiple storage registers 11 41 8 8
Command Message
Response Message
(During Normal Operation)
Response Message
(During Error)
Slave Address 02H Slave Address 02H Slave Address 02H
Function Code 03H Function Code 03H Function Code 83H
Start
Address
Upper bit 00H Data quantity 08H Error code 03H
Lower bit 20H Lead
storage
register
Upper bit 00H
CRC-16
Upper bit F1H
Quantity
Upper bit 00H Lower bit 65H Lower bit 31H
Lower bit 04H Next
storage
register
Upper bit 00H
CRC-16
Upper bit 45H Lower bit 00H
Lower bit F0H Next
storage
register
Upper bit 00H
Lower bit 00H
Next
storage
register
Upper bit 01H
Lower bit F4H
CRC-16
Upper bit AFH
Lower bit 82H
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