Store Multiple Setpoints; Exception Responses - GE Multilin 745 Communications Manual

CHAPTER 2: MODBUS PROTOCOL
Store multiple
setpoints

Exception responses

745 TRANSFORMER PROTECTION SYSTEM – COMMUNICATIONS GUIDE
Modbus implementation: Preset multiple registers
GE Multilin implementation: Store multiple setpoints
This function code allows the master to modify the contents of a one or more consecutive
setpoint registers in the addressed slave device. Setpoint registers are 16 bit (two byte)
values transmitted high order byte first. The maximum number of register values
(setpoints) that can be stored in a single message is 60.
For example, request slave device 11 to write the value 00C8 at setpoint address 1100, and
the value 0001 at setpoint address 1101.
Master query message
Slave address
Function code
Data starting address (high, low)
Number of setpoints (high, low)
Byte Count
Data #1 (high, low)
Data #2 (high, low)
CRC (low, high)
Slave response
Slave address
Function code
Data starting address (high, low)
Number of setpoints (high, low)
CRC (low, high)
Programming or operation errors happen because of illegal data in a message, hardware
or software problems in the slave device, etc. These errors result in an exception response
from the slave. The slave detecting one of these errors sends a response message to the
master consisting of slave address, function code, error code, and CRC. To indicate that the
response is a notification of an error, the high order bit of the function code is set to 1.
Table 2–2: Modbus error codes
Error Modbus definition
01 Illegal function
02 Illegal data address
03 Illegal data value
04 Failure in associated
device
05* Acknowledge
06* Busy, rejected
message
07* NAK - Negative
Acknowledge
* Some implementations of Modbus may not support these exception responses.
Example Description
11 query message for slave 11
10 store multiple setpoint values
11 00 data starting at address 1100
00 02 2 setpoint values = 4 bytes total
04 4 bytes of data
00 C8 data for address 1100 = 00C8
00 01 data for address 1101 = 0001
27 01 CRC computed by master
Example Description
11 response message from slave 11
10 store multiple setpoint values
11 00 data starting at address 1100
00 02 2 setpoint values = 4 bytes total
46 64 CRC computed by slave
GE Multilin implementation
The function code of the master query message is not a
function code supported by the slave.
The address referenced in the data field of the master query
message is not an address supported by the slave.
The value referenced in the data field of the master query
message is not allowable in the addressed slave location.
An external device connected to the addressed slave device
has failed and the data cannot be sent. This response will be
returned if a GE Multilin device connected to the RS485 external
device port of the 745 has failed to respond to the 745.
The addressed slave device has accepted and is processing a
long duration command. Poll for status.
The message was received without error, but the slave device is
engaged in processing a long duration command. Retransmit
later, when the slave device may be free.
The message was received without error, but the request could
not be performed, because this version of the 745 does not
have the requested operation available.
MODBUS PROTOCOL
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