Siemens SIMATIC NET CP 142-2, Manual, Page: 26 / 84

B8976111/02 AS-i Master Module CP 142-2
3-4
Figure 3-1 shows an example of how a slave is addressed by a user program with start addresses m
= 256 for the input data and n = 256 for the output data. The bits relevant for the user program are
shown on a gray background. The bits on a white background are irrelevant for the user program.
Slave No. 2 Slave No. 3 Slave No. 4
AS -i s la ve s
Bit 0 Bit 1 Bit 2 Bit 3
Slave 5
Bit 0 Bit 1 Bit 2 Bit 3
2 58
.
.
.
2 57
2 56
Bit 0 Bit 1 Bit 2
B it 3
Slave 2
Bit 0 Bit 1 Bit 2 Bit 3
Bit 0 Bit 1 Bit 2 Bit 3
Slave 4
Bit 0 Bit 1 Bit 2 B it 3
Slave 30
Bit 0 Bit 1 Bit 2 Bit 3
Slave
31
7 6 5 4 3 2 1 0
Slave No.31
Bit 0 Bit 1 Bit 2 Bit 3
Inp ut
b yte
Slave 1
reserved
Slave 31
2 7 1
Slave 3
Bit 0 Bit 1 Bit 2 Bit 3
Slave 5
Bit 0 Bit 1 B it 2 B it 3
2 5 8
.
.
.
257
256
Bit 0
B it 1
Bit 2 Bit 3
Slave 2
Bit 0 Bit 1 B it 2 B it 3
Bit 0 Bit 1 Bit 2 Bit 3
Slave 4
Bit 0
B it 1
Bit 2 Bit 3
Slave 30
Bit 0 Bit 1 Bit 2 Bit 3
Slave
31
7 6 5 4 3 2 1 0
Bit 0 Bit 1 Bit 2 Bit 3
O utput
byte
Slave 1
reserved
Slave 31
2 71
Slave 3
4I module
2I/2O module
4O module 4I/4O module
Figure 3-1 Mapping the Slave Addresses on the I/O Addresses
In the diagram above, the 2I/2O module (two inputs and two outputs) occupies bits 0 and 1 in input
byte 257 and bits 2 and 3 in output byte 257. The assignment of the AS-i connections of the bus
modules to the data bits of the input/output bytes is shown below taking slave no. 3 as an example:
1 0 Bit no.
Input byte 257
Connector 1 on the AS-i bus
module
Connector 2 on the AS-i bus module
3 2 Bit no.
Output byte 257
Connector 3 on the AS-i bus module
Connector 4 on the AS-i bus module
3.2.2 Accessing the AS-i User Data (BM141, BM142)
Access to the AS-i user data depends on the PROFIBUS master you are using. For further
information, refer to /4/.