GW Instek PFR Series Guide

Modbus RTU/TCP
PFR Series
START GUIDE
ISO-9001 CERTIFIED MANUFACTURER

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photocopied, reproduced or translated to another language without
prior written consent of Good Will company.
The information in this manual was correct at the time of printing.
However, Good Will continues to improve products and reserves the
rights to change specification, equipment, and maintenance
procedures at any time without notice.
Good Will Instrument Co., Ltd.
No. 7-1, Jhongsing Rd., Tucheng Dist., New Taipei City 236, Taiwan.

TABLE OF CONTENTS
3
Table of Contents
Overview ................................................................... 4
Quick guide function setting ..................................... 5
Modbus RTU .............................................................. 6
Introduction........................................................................................ 6
Using Modbus RTU .......................................................................... 8
Multiple Unit Connection ..............................................................10
Function check .................................................................................12
Modbus TCP ............................................................. 14
Introduction......................................................................................14
Using Modbus TCP.........................................................................16
Function check .................................................................................17
Data Type................................................................. 19
Char ....................................................................................................19
Uint16 ................................................................................................20
Uint32 ................................................................................................22
Float....................................................................................................23
Exception Code List .................................................. 25
Register List ............................................................. 27

Modbus RTU/TCP START GUIDE
4
Overview
This document serves as a comprehensive guide to the Modbus
functions. It begins with a “Quick Guide Function Setting”chapter,
offering users a straightforward method for rapid configuration.
The “Modbus RTU”chapter introduces the function codes, packet
formats, and setting steps of RTU, and provides practical examples.
Similarly, the chapter “Modbus TCP”explains that TCP has the
same function code as RTU, but its packet format is different. The
first address of the packet format is replaced by MBAP, and there is
no trailing CRC. This section also includes setup guidelines and
illustrative examples.
The “Data Type”section lists various data types used in Modbus,
accompanied by examples demonstrating their application.
Finally, the “Exception Code List”chapter is dedicated to outlining
the response codes for handling unexpected situations in Modbus
operations.
Note
This function is a non-standard function, and the
applicable firmware version must be higher than V1.33
(please refer to the user manual to check the firmware
version), and it needs to be activated or a license
purchased before the machine leaves the factory.
For more information, please contact your local dealer
or GW Instek at
www.gwinstek.com/[e-mail].

Quick guide function setting
5
Quick guide function setting
RTU
TCP
1. Connect PFR IN port to a PC
using RS485/RS232 cable
with DB9 & RJ-45.
2. Set the F-29 (Interface Select)
setting to 1 (RS232) or 2
(RS485).
3. Set UART Baud Rate (F-71).
4. Set the F-72 (UART Data Bits)
setting to 1 (8 bits).
5. Set UART Parity (F-73).
6. Set UART Stop Bit (F-74).
7. Set the F-75 (UART TCP)
setting to 2 (Modbus RTU).
8. Set UART Address
(Modbus Slave Address) (F-
76).
9. Set the F-77 (UART Multi-
Drop control) setting to 0
(Disable).
1. Connect an Ethernet cable
from the network to the rear
panel Ethernet port.
2. Set the F-29 (Interface Select)
setting to 8 (Modbus TCP).
3. Set IP address (F-39~F-42).
4. Set Subnet Mask (F-43~F-46).
5. Set Gateway (F-47~F-50).
NOTE:
Socket server port number is
502 for Modbus master
application.

Modbus RTU/TCP START GUIDE
6
Modbus RTU
Introduction
Overview
Modbus RTU message consists of Address and
PDU, ending with CRC.
Modbus data is transmitted in frames, and each
frame has a determined starting point and ending
point.
In RTU mode, a minimum 3.5-character pause is
required at the beginning of the message. After the
last character is sent, there will be a 3.5-character
pause before a new message can be sent.
Frame2
>= 3.5 char
…
>= 3.5 char
Frame1
Function code
The function codes provided for use are as
follows.
Function code
Description
0x03
Read Holding Registers
0x06
Write Single Registers
0x10
Write Multiple Registers
Read Holding
Registers
(FC 0x03)
Request:
Address
Function
code
Starting
registers
Number of
register
CRC
Byte0
Byte1
Byte2,3
Byte4,5
Byte6,7
Response:
Address
Function
code
Byte count
Data
CRC
Byte0
Byte1
Byte2
Byte3~252
Last1,2

Modbus RTU
7
Write Single
Registers
(FC 0x06)
Request:
Address
Function
code
Starting
registers
Data
CRC
Byte0
Byte1
Byte2,3
Byte4,5
Byte6,7
Response:
Address
Function
code
Starting
registers
Data
CRC
Byte0
Byte1
Byte2,3
Byte4,5
Byte6,7
Write Multiple
Registers
(FC 0x10)
Request:
Address
Function
code
Starting
registers
Number
count
Data
byte
CRC
Byte0
Byte1
Byte2,3
Byte4,5
Byte6
Byte7~
253
Last1,2
Response:
Address
Function
code
Starting
registers
Data
CRC
Byte0
Byte1
Byte2,3
Byte4,5
Byte6,7

Modbus RTU/TCP START GUIDE
8
Using Modbus RTU
Overview
The PFR power supply can use Modbus RTU
protocol via RS232 and RS485. RS232 and RS485
are using PSU-232 and PSU-485 to connect PC.
The pin outs for the adapters are shown below.
PSU-232 RS232
cable with DB9
connector
DB-9 Connector
Remote IN Port(RJ-45)
Remark
Pin No.
Name
Pin No.
Name
Housing
Shield
Housing
Shield
2
RX
7
TX
Twisted
pair
3
TX
8
RX
5
SG
1
SG
5 1
9 6
1 8
(RJ-45)
(DB-9)
PSU-485 RS485
cable with DB9
connector
DB-9 Connector
Remote IN Port(RJ-45)
Remark
Pin No.
Name
Pin No.
Name
Housing
Shield
Housing
Shield
9
TXD-
6
RXD-
Twisted
pair
8
TXD+
3
RXD+
1
SG
1
SG
5
RXD-
5
TXD-
Twisted
pair
4
RXD+
4
TXD+
5 1
9 6
1 8
(RJ-45)
(DB-9)

Modbus RTU
9
Diagram of End
terminal
connector
End terminal
connector from
PSU-232 or PSU-
485 connection
kit.
End terminal connector
8 Pin Connector
Pin No.
Remarks
3
Internal shorted
7
4
Internal shorted
8
Operation
1. Connect the RS232 serial cable
(include in the PSU-232
connection kit) or RS485 serial
cable (include in the PSU-485
connection kit) to the Remote IN
port on the real panel.
Connect the other end of the cable
to the PC.
RS 485 / 232 1
2. Connect the end terminal
connector (include in the PSU-232
or RS-485 connection kit) to the
Remote OUT port on the rear
panel.
RS 485 / 232
2
3. Press the Function key to enter the Normal
configuration settings.
Table
UART Menu
Menu
Function
Item
F-29
Interface
Select
0 = Disable, 1 = RS232, 2 = RS485,
3 = USB-CDC / NO Mass Storage,
4 = GPIB, 5 = LAN SOCKET,
6 = LAN WEB 7 = USB-TMC,
8 = Modbus TCP
F-71
UART Baud
Rate
0 = 1200, 1 = 2400, 2 = 4800,
3 = 9600, 4 = 19200, 5 = 38400,
6 = 57600, 7 = 115200

Modbus RTU/TCP START GUIDE
10
F-72
UART Data
Bits
0 = 7 bits, 1 = 8 bits
F-73
UART Parity
0 = None, 1 = Odd, 2 = Even
F-75
UART TCP
0 = SCPI, 1 = TDK (emulation
mode) 2 = Modbus RTU
F-76
UART Address
(Modbus Slave
Address)
01 ~ 30
F-77
UART Multi-
Drop control
0 = Disable, 1 = Master,
2 = Slave, 3 = Display information
Multiple Unit Connection
Operation
1. Connect the first unit’s IN port to a PC via
RS232 or RS485 serial cable.
Use the serial cables supplied in the PSU-232
or PSU-485 connection kit.
2. Plug in intermediate connector to the OUT port
on the first unit then using the slave serial link
cable (black plug) to connect intermediate
connector to the IN port of the second unit.
RS 485 / 232
OUT IN
Unit #1
RS 485 / 232
OUT IN
Unit #2
RS 485 / 232
OUT IN
Unit #N
End terminal
connector
To PC
RS232/RS485
serial cable
Slave serial
cable(black plug)
Slave serial
cable(black plug)
Intermediate
connector
3. Connect all the remaining units in the same
fashion until all the units have been daisy-
chained together.
4. Terminate the OUT port of the last unit with the
end terminal connector included in the PSU-
232 or PSU-485 connection kit.

Modbus RTU
11
5. Press the Function key to enter the Normal
configuration settings (Please refer to Table
UART Menu to set the UART related settings
where the UART address must be unique).
Slave serial link
cable with RJ-45
shielded
connectors from
PSU-232 or PSU-
485 connection
kit
RS-485 slave serial link pin assignment
8 Pin Connector
(IN)(RJ-45)
8 Pin Connector
(OUT)(RJ-45)
Pin No.
Name
Pin No.
Name
Housing
Shield
Housing
Shield
1
SG
1
SG
6
TXD -
6
TXD -
3
TXD +
3
TXD +
5
RXD -
5
RXD -
4
RXD +
4
RXD +
1 8
(RJ-45)
1 8
(RJ-45)
Diagram of
Intermediate
connector
Intermediate
connector from
PSU-232 or PSU-
485 connection
kit.
Intermediate connector
8 Pin (Male)
8 Pin (Female)
Pin No.
Name
Pin No.
Name
Remarks
Housing
Shield
Case
Shield
1
SG
1
SG
6
TXD -
6
TXD -
Internal paralleled
by 120 ohm
3
TXD +
3
TXD +
5
RXD -
5
RXD -
Internal paralleled
by 120 ohm
4
RXD+
4
RXD +

Modbus RTU/TCP START GUIDE
12
Diagram of End
terminal
connector
End terminal
connector from
PSU-232 or PSU-
485 connection
kit.
End terminal connector
8 Pin Connector
Pin No.
Remarks
3
Internal shorted
7
4
Internal shorted
8
Function check
Function check steps are as follows:
Functionality
Check
1. Connect PFR IN port to a PC using
RS485/RS232 cable with DB9 & RJ-45 (To check
the COM port No, see the Device Manager in
the PC).
2. Set PFR settings related to Modbus RTU (Please
refer to Table UART Menu to set the UART
related settings where the UART address must
be unique).
3. Invoke a Modbus RTU master application.
4. Use PC application to send an ADU package to
PFR (Please refer to the Register List).
For this function check, we will assume that
PFR’s Slave ID is assigned to 0x02.
Slave ID: 0x02
According to Modbus register list, we are using
“Identification register” to present this function
check.

Modbus RTU
13
Function Code: 0x03
Start Address: 0
Number of Register: 50
The request packet of ADU is as follows:
Address
Function
code
Starting
registers
Number of
register
CRC
Byte0
Byte1
Byte2,3
Byte4,5
Byte6,7
0x02
0x03
0x00 0x00
0x00 0x32
0xC4 0x2C
Slave
address
(F-76)
Read
Holding
Registers
Registers
address
Account for
50 registers
5. And instrument will Response:
Address
Function
code
Byte
count
Data
CRC
Byte0
Byte1
Byte2
Byte3~252
Last1,2
0x02
0x03
0x64
0x47 0x57
0x2D 0x49
0x4E 0x53
…0x00
0x00 0x00
0x59 0x79
Slave
address
(F-76)
Read
Holding
Registers
100 byte
GW-INSTEK
…

Modbus RTU/TCP START GUIDE
14
Modbus TCP
Introduction
Overview
Modbus TCP messages consist of MBAP header
and PDU. Different from RTU, there is no Slave
address and CRC.
Modbus TCP is based on Ethernet. Modbus TCP
socket port number is 502.
MBAP header
Transaction ID
Protocol ID
Length
Unit ID
Byte0,1
Byte2,3
Byte4,5
Byte6
Function code
The function codes provided for use are as follows.
Function code
Description
0x03
Read Holding Registers
0x06
Write Single Registers
0x10
Write Multiple Registers
Read Holding
Registers
(FC 0x03)
Request:
MBAP
header
Function
code
Starting
registers
Number of
register
Byte 0~6
Byte7
Byte8,9
Byte10,11
Response:
MBAP
header
Function
code
Length of
data
Data
Byte 0~6
Byte7
Byte8
Byte9~259
Write Single
Registers
(FC 0x06)
Request:
MBAP
header
Function
code
Starting
registers
Data
Byte 0~6
Byte7
Byte8,9
Byte10,11
Response:
MBAP
header
Function
code
Starting
registers
Data
Byte 0~6
Byte7
Byte8,9
Byte10,11

Modbus TCP
15
Write Multiple
Registers
(FC 0x10)
Request:
MBAP
header
Function
code
Starting
registers
Number of
register
Data
byte
Data
Byte 0~6
Byte7
Byte8,9
Byte10,11
Byte12
Byte13
~259
Response:
MBAP
header
Function
code
Starting
registers
Number of
register
Byte 0~6
Byte7
Byte8,9
Byte10,11

Modbus RTU/TCP START GUIDE
16
Using Modbus TCP
Overview
Modbus TCP is based on Ethernet. Modbus TCP
socket port number is 502. The Ethernet related
configurations are shown as Table Ethernet Menu
below.
Operation
1. Connect an Ethernet cable from the
network to the rear panel Ethernet
port.
2. Press the Function key to enter the Normal
configuration settings.
Table
Ethernet Menu
Menu
Function
Item
F-29
Interface Select
0 = Disable, 1 = RS232, 2 =
RS485,
3 = USB-CDC / NO Mass Storage,
4 = GPIB, 5 = LAN SOCKET,
6 = LAN WEB, 7 = USB-TMC,
8 = Modbus TCP
F-30
MAC Address-1
0x00~0xFF
F-31
MAC Address-2
0x00~0xFF
F-32
MAC Address-3
0x00~0xFF
F-33
MAC Address-4
0x00~0xFF
F-34
MAC Address-5
0x00~0xFF
F-35
MAC Address-6
0x00~0xFF
F-37
DHCP
0 = OFF, 1 = ON
F-39
IP Address-1
0~255
F-40
IP Address-2
0~255
F-41
IP Address-3
0~255
F-42
IP Address-4
0~255
F-43
Subnet Mask-1
0~255
F-44
Subnet Mask-2
0~255
F-45
Subnet Mask-3
0~255
F-46
Subnet Mask-4
0~255
F-47
Gateway-1
0~255
F-48
Gateway-2
0~255
F-49
Gateway-3
0~255

Modbus TCP
17
F-50
Gateway-4
0~255
F-51
DNS address-1
0~255
F-52
DNS address-2
0~255
F-53
DNS address-3
0~255
F-54
DNS address-4
0~255
Function check
Function check steps are as follows:
Functionality
Check
1. Connect an Ethernet cable from the network to
the rear panel Ethernet port.
2. Set PFR settings related to Modbus TCP (Please
refer to Table Ethernet Menu related settings).
3. Invoke a Modbus TCP master application.
4. Use PC application to send an ADU package to
PFR (Please refer to the Register List).
According to Modbus register list, we are using
“Identification register” to present this function
check.
Function Code: 0x03
Start Address: 0
Number of Register: 50

Modbus RTU/TCP START GUIDE
18
The request packets of MBAP header and ADU are
as follows:
MBAP header
Function
code
Starting
registers
Number of
register
Byte 0~6
Byte7
Byte8,9
Byte10,11
0x00 0x18
(Transaction ID)
0x00 0x00
(Protocol ID)
0x00 0x06(Length)
0x00 (Unit ID)
0x03
0x00 0x00
0x00 0x32
MBAP header
Read
Holding
Registers
Registers
address
Account for
50 registers
5. And instrument will Response:
MBAP header
Function
code
Length of
data
Number of
register
Byte 0~6
Byte7
Byte8
Byte9~259
0x00 0x18
(Transaction ID)
0x00 0x00
(Protocol ID)
0x00 0x06(Length)
0x00 (Unit ID)
0x03
0x00 0x64
0x47 0x57
0x2D 0x49
0x4E 0x53
…0x00
0x00 0x00
MBAP header
Read
Holding
Registers
100 byte
GW-INSTEK
…

Data Type
19
Data Type
Overview
This chapter will introduce the data package
format of each data type and provide data type
examples for reference. The following are the
types of data provided:
Char
Uint16
Uint32
Float
1 Byte
2 Byte
4 Byte
4 Byte
Char
Examples of character data types are as follows:
This example is to read the identification data,
refer to Register List as shown below:
The read identification function code is 0x03, the
starting register is 0, and the number of registers is
50.
Based on the above, the requested PDU is as
follows:
Function code
Starting registers
Number of register
0x03
0x00 0x00
0x00 0x32
Read
0 (Identification)
50 register (100
byte)
Response PDU:
Function code
Length of data
Data
0x03
0x64
0x47 0x57 0x2D
0x49 0x4E 0x53
… 0x00 0x00 0x00
Read
100 byte
GW-INSTEK…

Modbus RTU/TCP START GUIDE
20
Uint16
There are two value types of Uint16:
Normal value
This example is to read/write the Buzzer control,
refer to Register List as shown below:
The starting register for read/write buzzer control
is 801, and the number of registers is 1.
Based on the above, the PDU is as follows:
Write
Request PDU:
Function code
Starting registers
Data
0x06
0x03 0x21
0x00 0x01
Write
801(Buzzer on/ off)
Buzzer on
Response PDU:
Function code
Starting registers
Data
0x06
0x03 0x21
0x00 0x01
Write
801(Buzzer on/off)
Buzzer on
Read
Request PDU:
Function code
Starting registers
Number of
register
0x03
0x03 0x21
0x00 0x01
Read
801(Buzzer on/ off)
One register
Response PDU:
Function code
Length of data
Data
0x03
0x02
0x00 0x01
Read
2 byte
Buzzer on