MPA3 V6.3 MOTOR PROTECTION RELAY MANUAL
Issue: R0, Date: 11/2010, CRN: 8168
MPAB010 Rev0
MPA3 V6.2 Motor Protection Relay Manual
Page 18
13.1
Modbus Communications
13.1.1
Modbus Configuration
The baud rate is selected via the ‘
Modbus:
’ setting (Level 7, Position 25) and is selectable between 1200 and 9600
Baud, with even, odd, or no parity. One stop bit is used in conjunction with parity, while two stop bits are used with no
parity.
The half-duplex 3-wire RS485 communications interface allows up to 31 devices to be multi-dropped onto a single
master communication line. The MPA’s Modbus Slave address is selected via the ‘
Modbus Ad
:’ setting (Level 7,
Position 26) and is adjustable between 1 and 31.
13.1.2
Modbus Commands
The following Modbus commands are supported:
Modbus CMD
Comment
03
Read Holding Registers
04
Read Input Registers
06
Store Single Register
16
Store Multiple Registers
Valid read registers are in the range from 1 to 96. An attempt to read a register outside this range will result in an
exception scan. Currently, only the first 64 registers contain valid data. The range from 65 to 96 is for future
expansion The range from 65 to 96 are also write addresses, the only active write address is 65 which is folded back
to the read only address 20.
Supported Modbus exception responses are:
Modbus Exception
Comment
01
Illegal Function
02
Illegal Data Address
03
Illegal Data Value
13.1.3
Modbus Status
The MPA Modbus status is shown on the ‘MPA I/O Status Information’ Page, Level 5, Position 4 and indicates the
following:
Status
Comment
No Opt Card
No monitoring card installed
No Mbus RxD
Monitoring card installed, but there
has not been a valid Modbus
transaction in the last 30 seconds
Online…OK
Monitoring card installed, a valid
Modbus transaction has occurred
in the last 30 seconds
