GE 750 User manual

Note
750/760
Feeder Management Relay
GE
Grid Solutions
COMMUNICATIONS GUIDE
Software Revision: 7.4x
GE Multilin Part Number: 1601-0229-AB
GE Publication Code: GEK-106473K
*1601-0229-AB*

© 2016 GE Multilin Inc. All rights reserved.
The 750/760 Feeder Management Relay Instruction Manual for revision 7.4x.
750/760 Feeder Management Relay is a registered trademark of GE Multilin Inc.
The contents of this manual are the property of GE Multilin Inc. This documentation is
furnished on license and may not be reproduced in whole or in part without the permission
of GE Multilin Inc. The content of this manual is for informational use only and is subject to
change without notice.
Part number: 1601-0229-AB (October 2016)

Note
Safety Words and Definitions
The following symbols used in this document indicate the following conditions:
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NOTE
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practices, that are not related to personal injury.
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750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE TOC - V
Table of Contents
1.OVERVIEW OverviewProtocols........................................................................................................................... 1 - 1
Physical Layer ................................................................................................................................... 1 - 2
2.MODBUS
PROTOCOL
Description.......................................................................................................................................... 2 - 1
Data Link Layer................................................................................................................................. 2 - 1
CRC-16 Algorithm ............................................................................................................................ 2 - 2
Message Timing................................................................................................................................ 2 - 3
3.MODBUS
FUNCTIONS
Supported Modbus Function Codes........................................................................................ 3 - 1
Function Code 01h/02h: Read Binary Status...................................................................... 3 - 2
Function Code 03h/04h: Read Actual Values / Setpoints ............................................. 3 - 2
Function Code 05h: Execute Operation................................................................................. 3 - 3
Function Code 06H: Store Single Setpoint............................................................................ 3 - 5
Function Code 10H: Store Multiple Setpoints ..................................................................... 3 - 5
Exception Responses ..................................................................................................................... 3 - 6
Clock Synchronization of Multiple Relays ............................................................................ 3 - 7
4.MODBUS MEMORY
MAP
Reading the Event Recorder ....................................................................................................... 4 - 1
Reading Trace Memory................................................................................................................. 4 - 2
Reading the Data Logger ............................................................................................................. 4 - 4
Accessing Data via the User Map............................................................................................. 4 - 4
Memory Map Organization .........................................................................................................4-5
Memory Map...................................................................................................................................... 4 - 6
Data Formats...................................................................................................................................4 - 46
Data Formats Notes .....................................................................................................................4 - 65
5.DNP
COMMUNICATIONS
DNP 3.0 Device Profile Document............................................................................................ 5 - 1
DNP Implementation...................................................................................................................... 5 - 3
6.DNP POINT LISTS Binary Input / Binary Input Change........................................................................................ 6 - 1
Binary / Control Relay Output.................................................................................................... 6 - 3
Analog Input / Analog Input Change ...................................................................................... 6 - 5

TOC - VI 750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE

750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE 1 - 1
750/760 Feeder Management Relay
Chapter 1: Overview
GE
Grid Solutions
Over view
Over view Protocols
The 750/760 Feeder Management Relay communicates with other computerized
equipment such as programmable logic controllers, personal computers, or plant master
computers using either the AEG Modicon Modbus protocol or the Harris Distributed
Network Protocol (DNP), Version 3.0. Following are some general notes:
• The 750/760 relay always act as slave devices meaning that they never initiate
communications; they only listen and respond to requests issued by a master
computer.
• For Modbus, a subset of the Remote Terminal Unit (RTU) format of the protocol is
supported which allows extensive monitoring, programming and control functions
using read and write register commands.
• For DNP, the functionality is restricted to monitoring of essential relay data and control
of important relay functions. A complete description of the services available via DNP
may be found in the section DNP 3.0 Device Profile Document on page 5 - 1.
DNP is a complex protocol. As a consequence, it is not possible within the scope of this
manual to provide a description of the protocol's operation in anything approaching the
detail required to understand how to use it to communicate with the relay. It is strongly
recommended that interested users contact the DNP Users Group at http://www.dnp.org
to obtain further information:
Members of the DNP Users Group are eligible to receive complete descriptions of all
aspects of the protocol. The Users Group also operates a website (http://www.dnp.org)
where technical information and support is available.

1 - 2 750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE
PHYSICAL LAYER CHAPTER 1: OVERVIEW
Physical Layer
Both the Modbus and DNP protocols are hardware-independent so that the physical layer
can be any of a variety of standard hardware configurations including RS232, RS422,
RS485, fiber optics, etc. The 750/760 includes a front panel RS232 port and two rear
terminal RS485 ports, one of which can also be configured as RS422. Data flow is half
duplex in all configurations. Refer to the Serial Communications section in Chapter 3 of the
instruction manual for details on wiring.
Each data byte is transmitted in an asynchronous format consisting of 1 start bit, 8 data
bits, 1 stop bit, and possibly 1 parity bit. This produces a 10 or 11 bit data frame. This is
important for transmission through modems at high bit rates (11 bit data frames are not
supported by many modems at baud rates greater than 300).
The baud rate and parity are independently programmable for each communications
port. Baud rates of 300, 1200, 2400, 4800, 9600, and 19200 are available. Even, odd, and
no parity are available. See the Communications section in Chapter 5 of the instruction
manual for further details.
The master device in any system must know the address of the slave device with which it
is to communicate. The 750/760 will not act on a request from a master if the address in
the request does not match the relay's slave address (unless the address is the broadcast
address – see below).
A single setpoint selects the slave address used for all ports with the exception that for the
front panel port the relay will accept any address when the Modbus protocol is used. The
slave address is otherwise the same regardless of the protocol in use, but note that the
broadcast address is 0 for Modbus and 65535 for DNP. The relay recognizes and processes
a master request (under conditions that are protocol-specific) if the broadcast address is
used but never returns a response.
DNP may be used on, at most, one of the communications ports. Any port(s) not selected
to use DNP will communicate using Modbus. The S1 RELAY SETUP COMMUNICATIONS 
DNP DNP PORT setpoint is used to select which port will communicate using DNP.
The maximum time for a 750/760 relay to return a response to any (non-broadcast)
master request never exceeds 1 second.

750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE 2 - 1
750/760 Feeder Management Relay
Chapter 2: Modbus Protocol
GE
Grid Solutions
Modbus Protocol
Description
This section is dedicated to discussion of details of the Modbus protocol. As noted above,
specifics of DNP are best obtained directly from the DNP Users Group. Along with the
Device Profile Document, the DNP specification provides sufficient information for a user
to develop an interface should DNP wish to be used for communications with the relay.
Data Link Layer
Communications takes place in packets which are groups of asynchronously framed byte
data. The master transmits a packet to the slave and the slave responds with a packet. The
end of a packet is marked by ‘dead-time’ on the communications line. The following
describes general format of both transmit and receive packets. For exact details on packet
formatting refer to subsequent sections describing each function code.
The Modbus packet format is a set of five sequential information blocks:
Each block of the Modbus packet is described below:
•Slave Address: This is the address of the slave device intended to receive the packet
sent by the master and perform the desired action. Each slave device on a
Block Size
Slave Address 1 byte
Function Code 1 byte
Data nbytes, n≥1
Cyclic Redundancy Check (CRC) 2 bytes
Dead Time 3.5 bytes transmission time

2 - 2 750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE
CRC-16 ALGORITHM CHAPTER 2: MODBUS PROTOCOL
communication bus must have a unique address to prevent bus contention. All the
relay ports have the same address which is programmable from 1 to 254 (see the Port
Setup section in Chapter 5 of the instruction manual). Only the addressed slave will
respond to a packet that starts with its address. Note that the front port is an
exception to this rule; it will act on a message containing any slave address.
A master transmit packet with a slave address of 0 indicates a broadcast command.
All slaves on the communication link will take action based on the packet, but none
will respond to the master. Broadcast mode is only recognized when associated with
Function Codes 05h, 06h, and 10h. For any other function code, a packet with
broadcast mode slave address 0 will be ignored. See Clock Synchronization of Multiple
Relays on page 3-7 for an example of broadcast mode.
•Function Code: This is one of the supported functions codes of the 750/760 which tells
the slave what action to perform. See Supported Modbus Function Codes on page 3-1
for complete details. An exception response from the slave is indicated by setting the
high order bit of the function code in the response packet. See page 3–7 for further
details.
•Data: This will be a variable number of bytes depending on the function code. This
may include actual values, setpoints, or addresses sent by the master to the slave or
by the slave to the master.
•Cyclic Redundancy Check (CRC): This is a two byte error checking code. The RTU
version of Modbus includes a 16-bit cyclic redundancy check (CRC-16) with every
packet which is an industry standard method used for error detection. If a GE Multilin
Modbus slave device receives a packet in which an error is indicated by the CRC, the
slave device will not act upon or respond to the packet thus preventing any erroneous
operations. See the following section for a description of how to calculate the CRC.
•Dead Time: A packet is terminated when no data is received for a period of 3.5 byte
transmission times (about 15 ms at 2400 baud, 2 ms at 19200 baud). Consequently,
the transmitting device must not allow gaps between bytes longer than this interval.
Once the dead time has expired without a new byte transmission, all slaves start
listening for a new packet from the master except for the addressed slave.
CRC-16 Algorithm
The CRC-16 algorithm essentially treats the entire data stream (data bits only; start, stop
and parity ignored) as one continuous binary number. This number is first shifted left 16
bits and then divided by a characteristic polynomial (11000000000000101B). The 16 bit
remainder of the division is appended to the end of the packet, MSByte first. The resulting
packet including CRC, when divided by the same polynomial at the receiver will give a zero
remainder if no transmission errors have occurred. This algorithm requires the
characteristic polynomial to be reverse bit ordered. The most significant bit of the
characteristic polynomial is dropped, since it does not affect the value of the remainder.
Symbols: --> data transfer
A16 bit working register
Alow low order byte of A
Ahigh high order byte of A

CHAPTER 2: MODBUS PROTOCOL MESSAGE TIMING
750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE 2 - 3
CRC 16 bit CRC-16 result
i, j loop counters
(+) logical Exclusive OR operator
Ntotal number of data bytes
Dii-th data byte (i = 0 to N-1)
G16-bit characteristic polynomial = 1010000000000001(binary) with
MSbit dropped and bit order reversed
shr (x) right shift operator (the LSbit of x is shifted into a carry flag, a '0' is
shifted into the MSbit of x, all other bits are shifted right one
location)
The CRC algorithm is shown below.
1. FFFF (hex) --> A
2. 0 --> i
3. 0 --> j
4. Di(+) Alow --> Alow
5. j + 1 --> j
6. shr (A)
7. Is there a carry?
If No: go to step 8; if Yes: G (+) A --> A and continue.
8. Is j = 8? If No: go to 5; if Yes: continue.
9. i + 1 --> i
10. Is i = N? If No: go to 3; if Yes: continue.
11. A --> CRC
GE Multilin will provide a C programming language implementation of this algorithm upon
request.
Message Timing
Communication message synchronization is maintained by timing constraints. The
receiving device must measure the time between the reception of characters. If three and
one half character times elapse without a new character or completion of the message,
then the communication link must be reset (i.e. all slaves start listening for a new query
message from the master). Thus at 1200 baud a delay of greater than 3.5 ×1/
1200 ×10 = 29.2 ms will cause the communication link to be reset. At 9600 baud a delay
of greater than 3.5 ×1 / 9600 ×10 = 3.6 ms will cause the communication link to be reset.
Most master query messages will be responded to in less than 50 ms.

2 - 4 750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE
MESSAGE TIMING CHAPTER 2: MODBUS PROTOCOL

750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE 3 - 1
750/760 Feeder Management Relay
Chapter 3: Modbus Functions
GE
Grid Solutions
Modbus Funct ions
Supported Modbus Function Codes
Modbus officially defines function codes from 1 to 127 though only a small subset is
generally needed. The 750/760 relays support some of these functions, as summarized
below. Subsequent sections describe each function code in detail.
Table 1: GE Multilin Modbus Function Codes
Code Definition Description Substitute
Hex Dec
01 1
Read Binary Status Read one or more consecutive
binary status bits from the 750/760.
---
02 2 ---
03 3 Read Actual Values
Or Setpoints
Read actual value or setpoint
registers from one or more
consecutive memory map register
addresses.
04h
04 4 03h
05 5 Execute Operation Perform 750/760 specific
operations. 10h
06 6 Store Single
Setpoint
Write a specific value into a single
setpoint register. 10h
10 16 Store Multiple
Setpoints Write specific values into one or more consecutive setpoint registers. ---

3 - 2 750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE
FUNCTION CODE 01H/02H: READ BINARY STATUS CHAPTER 3: MODBUS FUNCTIONS
Function Code 01h/02h: Read Binary Status
These function codes allow the master to read one or more consecutive binary status bits
from an 750/760. The status bits are packed into bytes with the first addressed bit
occupying the least significant bit position of the first returned byte. Enough bytes are
returned to contain all requested status bits. The last byte is zero-padded as required. The
maximum number of status bits that can be read in a single request is 1920 (although this
greatly exceeds the number of status bits defined in the 750/760).
The addresses of the bits that can be read using these functions are the same as the point
indices defined for the DNP Binary Input objects (e.g., address zero references the “Relay In
Service” status). Refer to the DNP 3.0 Device Profile Document on page 5-1 for the definition
of all binary status data. Note that function codes 01H and 02H are identical in their
operation.
The following table shows the format of the master and slave packets. The example shows
a master device requesting 10 status bit values starting at address 13h from slave device
11; the slave device responds with the bit values 1, 0, 1, 1, 0, 0, 1, 0, 0 and 1 from binary
status addresses 13h through 1Ch inclusive. Note that two bytes are required to contain
the response data. The first byte contains the first eight data bits stored in the least
significant to the most significant bit position. The second byte contains the last two data
bits stored in the least two significant bit positions. Note that the rest of the second byte is
zero-filled.
Function Code 03h/04h: Read Actual Values /
Setpoints
This function code allows the master to read one or more consecutive data registers
(actual values or setpoints) from an 750/760. Data registers are always 16 bit (two byte)
values transmitted high-order byte first. The maximum number of registers that can be
read in a single packet is 120. See the section Modbus Memory Map on page 4-1 for exact
details on the data registers.
Master Transmission Bytes Example Description
Slave Address 1 11 message for slave 11
Function Code 1 01 read binary status
Data Starting Address 2 00 13 data starting at 0013h
Number of Data Bits 2 00 0A 10 data bits
CRC 2 4F 58 computed CRC error code
Slave Response Bytes Example Description
Slave Address 1 11 message from slave 11
Function Code 1 01 read binary status
Byte Count 1 02 2 bytes total
Data Bytes (high, low) 2 4D 02 value in address 0013h
CRC (low, high) 2 CC AE computed CRC error code

CHAPTER 3: MODBUS FUNCTIONS FUNCTION CODE 05H: EXECUTE OPERATION
750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE 3 - 3
Since some PLC implementations of Modbus only support one of function codes 03h and
04h, the 750/760 interpretation allows either function code to be used for reading one or
more consecutive data registers. The data starting address will determine the type of data
being read. Function Codes 03h and 04h are therefore identical.
The following table shows the format of the master and slave packets. The example shows
a master device requesting 3 register values starting at address 200h from slave device 11;
the slave device responds with the values 555, 0, and 100 from registers 200h, 201h, and
202h respectively.
Function Code 05h: Execute Operation
This function code allows the master to perform various operations in the 750/760.
Operations are shown in the Summary of Operation Codes for Function 05h table.
The following table shows the format of the master and slave packets. The example shows
a master device requesting the slave device 11 to perform a reset. The ‘high’ and ‘low’
Code Value bytes always have the values FFh and 00h, respectively and are a remnant of
the original Modbus definition of this function code.
Master Transmission Bytes Example Description
Slave Address 1 11 message for slave 11
Function Code 1 03 read register values
Data Starting Address 2 02 00 data starting at 0200h
Number of Registers 2 00 03 3 registers = 6 bytes total
CRC (low, high) 2 06 E3 computed CRC error code
Slave Response Bytes Example Description
Slave Address 1 11 message from slave 11
Function Code 1 03 read register values
Byte Count 1 06 3 values = 6 bytes total
Data #1 (high, low) 2 02 2B value in address 0200h
Data #2 (high, low) 2 00 00 value in address 0201h
Data #3 (high, low) 2 00 64 value in address 0202h
CRC (low, high) 2 C8 BA computed CRC error code
Master Transmission Bytes Example Description
Slave Address 1 11 message for slave 11
Function Code 1 05 execute operation
Operation Code 2 00 01 remote reset
Code Value 2 FF 00 perform operation
CRC (low, high) 2 DF 6A computed CRC error code
Slave Response Bytes Example Description
Slave Address 1 11 message from slave 11
Function Code 1 05 execute operation

3 - 4 750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE
FUNCTION CODE 05H: EXECUTE OPERATION CHAPTER 3: MODBUS FUNCTIONS
Operation Code 2 00 01 remote reset
Code Value 2 FF 00 perform operation
CRC (low, high) 2 DF 6A computed CRC error code
Slave Response Bytes Example Description
Table 2: Summary of Operation Codes for Function 05h
Operation
Code Definition Description
0000h No Operation Does not do anything.
0001h Reset Performs the same function as the front panel RESET key.
0002h Open Breaker Performs the same function as the front panel OPEN key. The 760 must be in
Remote Mode for this operation to be effective.
0003h Close Breaker Performs the same function as the front panel CLOSE key. The 760 must be
in Remote Mode for this operation to be effective.
0004h Set Time Sets the internal clock time. See page 3–7 for details.
0005h Set Date Sets the internal clock date. See page 3–7 for details.
0006h Trigger Trace Memory Performs the same function as the logic input function TRIGGER TRACE
MEMORY.
0007h Clear Energy Use Data Performs the same function as CLEAR ENERGY USE DATA command.
0008h Clear Max Demand Data Performs the same function as the CLEAR MAX DMD DATA command.
0009h Clear Event Recorder Data Performs the same function as the CLEAR EVENT RECORDER DATA
command.
000Ah Reset Trip Counter Data Performs the same function as the RESET TRIP COUNTER DATA command.
000Bh Reset Arcing Current Data Performs the same function as the RESET ARCING CURRENT DATA
command.
000Ch Display Override Packet Displays the 40 character (20 register) Override_Packet (addresses 10B1 to
10C4 hex) for the time specified in Override_Time (address 10B0 hex).
000Dh Trigger Data Logger Performs the same function as the logic input function TRIGGER DATA
LOGGER.
000Eh Reset Trace Memory Resets the Trace Memory oscillography data by clearing the number of
captured events to zero.
000Fh Reset Data Logger Resets the Data Logger by clearing the number of captured events to zero.
0010h Reset Ar Count Data Resets the Autoreclose Count by setting the AR SHOT COUNT to zero.
0011h Reset Ar Rate Data Resets the Autoreclose Shot Rate by setting AR SHOT RATE to zero.

CHAPTER 3: MODBUS FUNCTIONS FUNCTION CODE 06H: STORE SINGLE SETPOINT
750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE 3 - 5
Function Code 06H: Store Single Setpoint
This function code allows the master to modify the contents of a single setpoint register in
a 750/760. Setpoint registers are always 16 bit (two byte) values transmitted high-order
byte first (see the section Modbus Memory Map on page 4-1 for details). The following table
shows the format of the master and slave packets. It shows a master device storing the
value 200 at memory map address 1100h to slave device 11.
Function Code 10H: Store Multiple Setpoints
This function code allows the master to modify the contents of a one or more consecutive
setpoint registers in a 750/760. Setpoint registers are 16 bit (two byte) values transmitted
high-order byte first. The maximum number of setpoint registers that can be stored in a
single packet is 60. The table below shows the format of the master and slave packets. It
shows a master device storing the value 200 at memory map address 1100h, and the
value 1 at memory map address 1101h to slave device 11.
Master Transmission Bytes Example Description
Slave Address 1 11 message for slave 11
Function Code 1 06 store single setpoint
Data Starting Address 2 11 00 data starting at 1100h
Data 2 00 C8 data for address 1100h
CRC (low, high) 2 8F F0 computed CRC error code
Slave Response Bytes Example Description
Slave Address 1 11 message from slave 11
Function Code 1 06 store single setpoint value
Data Starting Address 2 11 00 data starting at 1100h
Data 2 00 C8 data for address 1100h
CRC (low, high) 2 8F F0 computed CRC error code
Master Transmission Bytes Example Description
Slave Address 1 11 message for slave 11
Function Code 1 10 store multiple setpoint value
Data Starting Address 2 11 00 data starting at 1100h
Number of Setpoints 2 00 02 2 setpoints = 4 bytes total
Byte Count 1 04 4 bytes of data
Data #1 2 00 C8 data for address 1100h
Data #2 2 00 01 data for address 1101h
CRC (low, high) 2 27 01 computed CRC error code
Slave Response Bytes Example Description
Slave Address 1 11 message from slave 11
Function Code 1 10 store multiple setpoint value

3 - 6 750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE
EXCEPTION RESPONSES CHAPTER 3: MODBUS FUNCTIONS
Exception Responses
Programming or operation errors happen because of illegal data in a packet, hardware or
software problems in the slave device, etc. These errors result in an exception response
from the slave. The GE Multilin 750/760 implements the error codes listed below. The slave
detecting one of these errors sends a response packet to the master with the high-order
bit of the function code set to 1. The following table shows the format of the master and
slave packets. The example shows a master device sending the unsupported function
code 39h to slave device 11.
Data Starting Address 2 11 00 data starting at 1100h
Number of Setpoints 2 00 02 2 setpoints = 4 bytes total
CRC (low, high) 2 46 64 computed CRC error code
Slave Response Bytes Example Description
Master Transmission Bytes Example Description
Slave Address 1 11 message for slave 11
Function Code 1 39 unsupported function code
CRC (low, high) 2 CD F2 computed CRC error code
Slave Response Bytes Example Description
Slave Address 1 11 message from slave 11
Function Code 1 B9 return unsupported function
code
Data Starting Address 2 11 00 data starting at 1100h
Number of Setpoints 2 00 02 2 setpoints = 4 bytes total
CRC (low, high) 2 93 computed CRC error code
Table 3: Exception Response Error Codes
Error
Code Modbus Definition GE Multilin Implementation
01 Illegal Function The function code of the master query message is not supported by the
slave.
02 Illegal Data Address The address referenced in the data field of the master query message is not
an address supported by the slave.
03 Illegal Data Value The value referenced in the data field of the master query message is not
allowable in the addressed slave location.
04 Failure In Associated Device
An external device connected to the addressed slave device has failed and
the data requested 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 750/760.
* Some Modbus implementations may not support these exception responses

CHAPTER 3: MODBUS FUNCTIONS CLOCK SYNCHRONIZATION OF MULTIPLE RELAYS
750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE 3 - 7
Clock Synchronization of Multiple Relays
The time and date of multiple relays on the same communication link can be synchronized
so that time stamping of events on different relays can be correlated. The following
procedure describes how to synchronize the clocks of multiple relays. Since the clock is
accurate to 1 minute per month, performing this procedure every 10 minutes will result in
synchronization accuracy of ±10 ms.
1. Store values for the date and time setpoints Set Date and Set Time at locations 1006h
and 1008h in the Memory Map respectively into each slave device.
2. Broadcast (via slave address 0) the Set Date operation code via function code 05h to
all connected slaves to synchronize the dates.
3. Broadcast (via slave address 0) the Set Time operation code via function code 04h to
all connected slaves to synchronize the times. If synchronizing to an external clock
source then this command should be sent when the time is equal to the value stored
in Set Time.
The following table shows the format of the master and slave packets for a master device
storing the date of June 10, 1994 and time of 2:15:30 PM to slave device 11 as required by
step one of the procedure.
05* Acknowledge The addressed slave device has accepted and is processing a long duration
command. Poll for status.
06* Busy, Rejected Message
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.
07* Nak - Negative
Acknowledge
The message was received without error, but the request could not be
performed, because this version of the 750/760 does not have the
requested operation available.
Table 3: Exception Response Error Codes
Error
Code Modbus Definition GE Multilin Implementation
* Some Modbus implementations may not support these exception responses
Master Transmission Bytes Example Description
Slave Address 1 11 message for slave 11
Function Code 1 10 store multiple setpoints
Data Starting Address 2 10 06 data at address 1100h
Number Of Setpoints 2 00 04 4 setpoints = 8 bytes total
Byte Count 1 08 8 bytes of data
Data #1 2 06 0A month = 06h (June), day = 0Ah (10)
Data #2 2 07 CA Year = 07CAh (1994)
Data #3 2 0E 0F Time (hr:min) = 0Eh:0Fh (14:15)
Data #4 2 75 30 Time (ms) = 7530h (30000 ms = 30 s)
CRC (Low, High) 2 37 0C computed CRC error code

3 - 8 750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE
CLOCK SYNCHRONIZATION OF MULTIPLE RELAYS CHAPTER 3: MODBUS FUNCTIONS
The following table shows the format of the master and slave packets for a master device
sending the Store Time operation code to all slave devices on the communications link as
required by step three of the procedure.
Slave Response Bytes Example Description
Slave Address 1 11 message from slave 11
Function Code 1 10 store multiple setpoints
Data Starting Address 2 10 06 data starting at 1006h
Number of Bytes 2 00 08 4 setpoints = 8 bytes total
CRC (low, high) 2 27 9B computed CRC error code
Master Transmission Bytes Example Description
Slave Address 1 11 message for slave 11
Function Code 1 05 execute operation
Operation Code 2 00 04 set time
Code Value 2 FF 00 perform operation
CRC (Low, High) 2 CC 2A computed CRC error code
Slave Response Bytes Example Description
No response from slave.