A.3 Communication Facilities Appendix A: Communication
286 493-0736-11 (6-2)
Data Characters – This section of the message contains the transmitted
characters specified by the Number of Characters. The value in the 16 bit registers
are sent in two bytes. Byte 1 which is sent second is the data character with the
lowest number. The bits in the register are sent in reverse order. The most
significant bit in the register is sent as the least significant bit of byte 2, as shown
in the example. The least significant bit in the register is the most significant bit
of byte 1.
Example: The value loaded in register A is:
ETX – End of text (03H), indicates the end of message.
BCC – block check count. This is a checksum calculated as the module 2 addition
(XOR) of each character in the message, except the initial STX-character.
A.3 Communication Facilities
A supervisory control system can read and write bits or register words located in
the communication memory area of the ECA controller (see "Communication
Area Mapping", on page cclxxxv). The communication facilities are listed below.
• All available analog and digital signal values can be read by a supervisory
system. The signals must be connected via communications buffers of type
AOC (Analog Output Communication) and DOC (Digital Output
Communication).
30
10
32
9
24=18H=
0
0
0
0
0
0
8
11111111111
15
1
111
1111111
111111
15
7
7
8
7FFD (50%)
Byte 1 Byte 2
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