GE Industrial Solutions MX150_MX250 Modbus Network Card - Manual (Page 3)

These bits make up the least significant byte of the Status
0 register, while the most significant byte of the Status 0
register contains zeros. Figure 1 shows an example of what
the Master device would see if it read back the entire
Status 0 register. In this example, the Master device would
read back the decimal value of 129 from the Status 0 reg-
ister. When this value is decoded, the Master finds out
that the S1 source is available and the Automatic Transfer
Relay input is active. The Master also has the option of
reading the individual bits, indented under Status 0. This
allows the Master to know the status of each parameter
without doing any decoding. The second column con-
tains the actual addresses for the network variables. These
addresses are used when the Master is reading a Holding
Register (16-bit reg). The third column contains address-
es that are used when the Master is reading a Coil (indi-
vidual bit). The remaining columns show the values and
ranges (only in Appendix B) for the
network variables.
LED Indicator
The Modbus card has a
10-segment LED module
(Refer to Appendix E
for location). These
LED’s display the slave
address of the card as well
as transmit and receive
status. The first LED from
the bottom indicates the
receive status, the second
LED indicates the transmit
status. When a Modbus
packet has been success-
fully transmitted or
received, the associated
LED will light for 100ms. If
another packet is sent or received before the 100ms elaps-
es, the LED on-time will be extended by another 100ms.
LED’s 3-10 display the slave address of the controller as
a binary number with each LED corresponding to a bit.
Figure 2 shows the 10-segment LED module along with
LED’s 3, 5, and 6 being lit. The lit LED’s correspond to
slave address 13.
■ ■ GE Zenith Controls 1 ■ ■ MX150/MX250 Series Modbus Network Card (71R-2200)
The Modbus network card is designed for the MX150
and MX250 controllers, version 6.0 program and above.
If the controller is ordered with the Modbus option, the
Modbus card will reside on the back of the controller
board and it will be part of the controller assembly. The
purpose of this card is to allow the controller to be avail-
able on a Modbus network as a slave device. This allows a
master device, such as a programmable logic controller
(PLC), to obtain information from the controller and
have that information available for control, data acquisi-
tion and monitoring.
Every Modbus network consists of one master device
and at least one slave device. All devices on the network
are daisy-chained using a twisted pair cable (see
Appendix E). Each slave device is assigned a unique
address from 1-247. Factory default for each Modbus
card is Slave Address 1. This address enables the master
to distinguish between the various slaves on the net-
work. It also allows the master device to send a query
command to the addressed slave. When the addressed
slave receives this command it will send back an appro-
priate response to the master. Table 1 shows a list of
Modbus commands which the Modbus network card
supports. Reference Appendix G for a more detailed
description of the Modbus commands.
The Modbus commands allow the master device to read
data from, and write data to, specific memory locations in
the controller. These memory locations, which are listed
in Appendix A and B, make up the Modbus network
variables. These variables allow the reading of controller
status, configuration, etc. The variables which can be
written to (reference Appendix B), include timer values,
Fail/Restore settings, and control variables.
Both lists contain a parameter name column that displays
the name of the memory locations. The non-indented
names in that column are 16-bit registers while the indented
ones are individual bits, which make up the 16-bit registers.
For example, Status 0, a non-indented name, is a 16-bit
register that consists of the following bits:
Overview
Modbus Command Modbus Command Description
01 Read Coil Status
03 Read Holding Register
05 Write Single Coil
06 Write Single Holding Register
15 Write Multiple Coils
16 Write Multiple Holding Registers
Table 1 – Supported Modbus Commands
0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1
Most Significant Byte
Normal Source Available
Least Significant Byte
Emergency Source Available
Load, No Load, Fast Load Test Status
Load Test Running
Not Used
Alarm
ATS Not in Auto Mode
Automatic Transfer Relay
Figure 1 – Status 0 Register
• S1 Available
• S2 Available
• Load, No Load, Fast
Load Test Status
• Load Test Running
• Alarm
• ATS Not in Auto Mode
• Automatic Transfer Relay
LED 9 - 2 6
LED 10 - 2 7
LED 8 - 2 5
LED 7 - 2 4
LED 6 - 2
3
LED 5 - 2 2
LED 4 - 2 1
LED 3 - 2 0
LED 2 - Transmit
LED 1 - Receive
Figure 2 – LED Module