13 (70)
3.5.2
Application Data (ADIs)
As mentioned previously, the total number of ADIs that can be represented on the network de-
pends on their size. By default, ADIs with instance numbers 1...3839 can be accessed from the
network, each with a size of up to 32 bytes. It is possible to alter this ratio by changing the num-
ber of ADI indexing bits. See attribute #9, in the
Modbus Host Object (FAh), p. 41
.).
Example 1 (Default Settings)
In this example, attribute #9 in the Modbus Host Object (FAh) is set to its default value (04h).
Holding Register #
ADI No.
1010h... 101Fh
1
1020h... 102Fh
2
1030h... 103Fh
3
1040h... 104Fh
4
...
...
FFE0h... FFEFh
3838
FFF0h... FFFFh
3839
Each ADI is represented using 16 Modbus registers, which means that up to 32 bytes of an ADI
can be accessed from the network.
Example 2 (Customized Implementation)
In this example, attribute #9 in the Modbus Host Object (FAh) is set to 05h.
Holding Register #
ADI No.
1010h... 102Fh
1
1030h... 104Fh
2
1050h... 106Fh
3
1070h... 108Fh
4
...
...
FFB0h... FFCFh
1918
FFD0h... FFEFh
1919
Each ADI is represented using 32 Modbus registers, which means that up to 64 bytes of an ADI
can be accessed from the network.
3.5.3
Process Data
Modbus does not feature a dedicated cyclic data channel in the same sense as many other net-
works. In the Anybus CompactCom 40 implementation, process data can however still be ac-
cessed from the network via dedicated entries in the Modbus register map.
Process data can be accessed on a bit by bit basis (as Coils & Discrete Inputs) -
or
- as 16 bit
entities (Holding Registers & Input Registers).
For natural reasons, writing to the write process data register area has no effect, and reading un-
used register locations will return zeroes.
Example
Each 16-bit Modbus register contains 2 bytes from the process data at the corresponding ad-
dress, i.e. Modbus register N holds process data byte (N*2) in the low byte and (N*2 + 1) in the
high byte.
Anybus
®
CompactCom
™
40 Modbus-TCP
®
Transparent Ethernet Network Guide
SCM-1202-022 1.1