ABB AC 31 - 1.3.4. Example using the MODBUS function

Communication
ABB Control - AC 31 Page 7-9
1SBC 260400 R1001-b 06.99
1.3.4. Example using the MODBUS function
An example of MODBUS communication between two 40 series central units.
40 series
MOD BU S
master
MODBUS protocol
RS232 line
40 series
MODBUS
slave 1
- A program isn't required in the slave central unit.
- A program example in the master central unit:
Read the 6 bits I62.00 to I62.05 in the slave 1 central unit.
The information is placed in O62.00 to O62.05 of the master central unit.
The MODBUS address of variable I62.00 in the slave 1 is 992 in decimal.
A delay should be defined to enable re-sending the MODBUS message in case of error. This
delay is called TIME_OUT and is generally 2 seconds.
ERROR_CODE
ERROR
READY
%O62.00
6
992
TIME_2S
READ_BITS
SLAVE_1
READY
MODBUS
FREI
SLAV
FCT
TIME
ADDR
NB
DATA
RDY
ERR
ERN
In case of MODBUS communication between one master 50 serie central unit and different
slaves 50 series central units, different MODBUS functions can be used. It is possible to link
them together to optimize the refresh time.
Check example : Read 6 bits continuously I62.00 to I62.05 in the slave 1 central unit. The
information is placed in O62.00 to O62.05 of the master central unit. W rite 20 words continuously
IW02.00 to IW02.19 in the slave 2 central unit. The information is received from master central
unit in MW00.00 to MW00.19.
MODBUS
FREI
S
LAV
F
C
T
TIME
A
DDR
NB
DAT
A
RDY
ERR
ERN
SLAVE_1
READ_BITS
TIME_2S
992
6
%O62.00
ERROR1
ERROR_CODE1 MODBUS
FREI
S
LAV
F
C
T
TIME
A
DDR
NB
DAT
A
RDY
ERR
ERN
SLAVE_2
WRITE_WORDS
TIME_2S
0000
20
%MW000.00
ERROR2
ERROR_CODE2