Honeywell HC900 - Manual (Page 40)

32 HC900 Hybrid Controller Communications User Guide Revision 10
12/07
4.6 Function Code 04 - Read Input Registers
Description
Function code 04(3X references) provides read access to Analog Input modules positioned in any Rack or
Slot. All values are in IEEE 32-bit floating point format.
For HC900 CPUs and Scanners with firmware version 2.3 and earlier, each Rack is allocated space for a
maximum of 16 Slots and each Slot assumes Modules with a maximum of 8 Channels, which consumes 16
Modbus Register addresses. See Table 4-9.
For HC900 CPUs and Scanners with firmware version 2.4 and higher, each Rack is allocated space for a
maximum of 16 Slots and each Slot assumes Modules with a maximum of 16 Channels, which consumes
32 Modbus Register addresses. See Table 4-10.
In Table 4-9 and Table 4-10 the register addressing is 1-based while the hex addressing is 0-based.
Table 4-9 HC900 AI Address Mapping supported by Function Code 04 (v2.3)
Rack Channels Register Range
(decimal)
Hex
Address Range
1 1 - 128 1 - 255 0 –FE
2 129 - 256 257 - 511 100 - 1FE
3 257 - 384 513 - 767 200 - 2FE
4 385 - 512 769 - 1023 300 - 3FE
5 513 - 640 1025 - 1279 400 - 4FE
Table 4-10 HC900 AI Address Mapping supported by Function Code 04 (v2.4 and higher)
Rack Channels Register Range
(decimal)
Hex
Address Range
1 1 – 256 2001 – 2511 0 -9CE
2 257 - 512 2513 – 3023 9D0 – BCE
3 513 - 768 3025 – 3535 BD0 – DCE
4 769 - 1024 3537 – 4047 DD0 – FCE
5 1025 - 1280 4049 - 4559 FD0 – 11CE
If a request is made to an address that does not exist in the map in Section 1, the controller will honor that
request and return zeros for that address. This behavior will greatly enhance the bandwidth on the link vs.
making several different requests for non-contiguous data elements. (i.e. Consider a controller that is
configured for AI #1 and AI #3 and for some reason AI #2 is an invalid request.) The contiguous method
would allow the read of AI #1 through AI #3 and the data location for AI #2 would be zeros.
Broadcast is not supported.