Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 12 Page 28 of 265
2.10 Maximum Number of I/O Cards and Intelligent Detector Backplanes
The total number of I/O cards and Intelligent Detector Backplanes that can be fitted
to the ST900 Controller is limited by the current capability of the power supply fitted
to the MDU. See Table 2 for details on the mix of cards that can be fitted to the
controller.
Table 2 applies where an IRM/IMU card is fitted (as this draws power from the 24
Volt rail)
The total maximum number of IO (the sum of loop inputs, digital inputs and digital
outputs) that can be configured cannot exceed 248 (31 8-bit ports).
Each IO card takes either 3, 4 or 5 8-bit ports (24-in 0 out, 24-in 4 out and 24 in 16
out)
Each Backplane Card takes 2 8-bit ports.
As an example, 7 backplanes and 6 IO cards could be configured as:
7 x backplanes 14 ports
2 x 24-in 16-out IO cards 10 ports
1 x 24-in 4-out IO card 4 ports
1 x 24-in 0-out IO card 3 ports
Total 31 ports
Number Of
Backplanes
Required
Maximum
Number Of
I/O Cards
Maximum
Number Of
Loop
Inputs
Maximum
Number Of
Digital
Inputs
Maximum
Number Of
Digital
Outputs
0 8 0 192 128
1 8 16 192 128
2 8 32 192 128
3 7 48 168 112
4 7 64 168 112
5 7 80 168 112
6 6 96 144 96
7 6 112 144 96
8 6 128 144 96
9 5 144 120 80
10 5 160 120 80
11 4 176 96 64
12 3 192 72 48
13 2 208 48 32
14 1 224 24 16
15 0 240 0 0
Table 1 – I/O Card and Detector Backplanes (ST900)
Without an IRM/IMU Card fitted.