Communication
Page 7-6 ABB Control - AC 31
1SBC 260400 R1001-b 06.99
1.3. Programming
1.3.1. MODBUS slave unit
All the data may be read or written in MODBUS . A program isn’t required for MODBUS
communication management. The MODBUS slave central unit automatically converts the
request sent by the master MODBUS and returns a message once it has recognized the
address.
The SINIT function is only required in the program when changing communication parameters.
1.3.2. MODBUS master unit
The MODBUS function enables sending data read / write requests to MODBUS
slaves
A change of communication parameters also requires the usage of the SINIT function in the
program.
1.3.3. List of cross references
An exchange of MODBUS data is realized in a table defined by:
- The MODBUS address of the first exchanged variable
- The list size = the total number of variables in the list.
All the variables of the 40 and 50 series central units, as described in the following table, can
be read or written by the master MODBUS .
- MODBUS
addressing method :
VAR 00.00 ADDR 0
(VAR = type I,O,S,M,IW,OW,MW,KW) (Address of the first selected variable in
decimal)
VAR XX.YY = ADDR 0 + ( 16 * XX ) + YY
(VAR = type MD,KD) (Address of the first selected variable in decimal)
VAR XX.YY = ADDR 0 + ( 32 * XX ) + ( 2 * YY )
Example : Find the MODBUS
address of variables O62.15 and M232.01 and MD002.07
O 62.15 = 4096 + ( 16 * 62 ) + 15 = 5103
M 232.01 = 8192 + ( 16 * 232 ) + 1 = 11905
MD002.07 = 4000 + ( 32 * 2 ) + ( 2 * 7 ) = 16462
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