ABB S900 Manual page 15

module or channel. The module slots can be assigned as required. However,
the total amount of input data and output data is limited to 244 bytes, each.
Note that the total amount of I/O data resulting from additional
communication services (parameters, diagnostics, non-cyclic services) must
not exceed 216 bytes for S900.
These limitations are specified in the GSD file (generic slave data file)
available for S900. They are monitored by the configuring instance.
Table 3-1 Data of different I/O modules
I/O modules
DO910
DX910
AO910
AI910
AI950
If no cyclic HART secondary variables are to be transmitted, no system
limitations result from this, since the max. possible amount of I/O data is
always less than 216 bytes, with 8 bytes per module and a total of 16
modules. Thus, an I/O System S900 station can in any case handle up to 16
I/O modules.
However, the total number of transmittable HART variables is limited, due to
the 216 bytes limit. With HART-compatible I/O modules (e.g. AI930) up to 8
HART variables can be transmitted with the cyclic data for each module.
HART variables are 32-bit floating point numbers occupying 4 bytes.
Calculating example:
Table 3-2 Example of I/O byte calculation
Configuration
CI020
6 x AI930
4 x AO910
6 x DX910
Total
3BDD010422R0101
Communication Interface for PROFIBUS DP, CI920
I/O data and
status [bytes]
1
3
8
8
8
Input [bytes]
0
6 x 8
0
6 x 2
60
I/O System S900
Output [bytes]
0
0
4 x 8
6 x 1
30
15