ABB ICMK14F1

Advant Controller AC 31 / Issued: 01.99 6 – 11 Communication
3
Example of the use of the MODBUS
®
function
An example of the use of MODBUS
®
communication between two 40 series basic units.
40 series
MODBUS
master
MODBUS protocol
RS-232 line
40 series
MODBUS
slave 1
- A program is not required in the MODBUS
®
slave basic unit.
- Example of a program in the MODBUS
®
master basic unit:
Read the 6 bits E62,00 to E62,05 in the MODBUS
®
slave 1 basic unit .
The information is written to A62,00 to A62,05 of the AC31 MODBUS
®
master basic unit.
The MODBUS
®
address of variable E62,00 in slave 1 is 992 as a decimal value.
MW0,0
M0,1
M0,0
AW62,00
KW1,4 = 6
KW1,3 = 992
KW1,2 = 2
KW1,1 = 2
KW1,0 = 1
M0,0
MODBUS
FREI
SLAV
FCT
TIME
ADDR
NB
DATA
RDY
ERR
ERN
A delay should be programmed so that the MODBUS
®
message can be sent again in the event
of an error. This delay is called TIME_OUT and is usually 2 seconds.
6.2.4 Response times for MODBUS
®
communication
The MODBUS
®
processing time depends on the following factors:
- Baud rate
- Number of frame bytes
- Basic unit cycle time
- Basic unit load factor
The following times are only given as guidelines.
Response times for a 40 or 50 series basic unit
Cycle time = 10 ms
Load factor = 80%
Baud rate = 9,600 baud