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Appendix A: Communication
The destination address would appear as:
24=18H=
Stamp – A character that changes value between message so that the slave station
can determine if it is a retransmission. The first message after starting must have
the value 30H. After the initial message, STAMP must alternate between 31H and
32H.
Stamp from the controller is always assigned the same value as Stamp from the
master (STAMPM) in the correctly received message. This means that Stamp and
Stamps are always different for each new message.
If at any time they are the same, the controller knows that the message type is a
retransmission and does not process the data.
Message type – Message position 4 reflects the message type being sent.
Start Address – Four charachters indicating the starting address of the memory
location, or registers in the controller where data retrieval is to begin. Each
controller register holds two bytes (16 bits). Therefore, register addresses must be
evenly divisible by 16.
Formula: Address = (16 × register number)H + 4000H (register 0).
Example: Calculate the address for register 16.
16 × 16 = 256(Decimal) = 100
100H + 4000H = 4100H
4100H = ASCII 34H, 31H, 30H, 30H
34
Number of Characters – This part of the message is a count of the number of
data bytes or characters sent in the message. The example below shows the ASCII
code for 32 bytes.
493-0736-11 (6-2)
Message byte number
1
31
5
6
7
8
31
30
30
2
38
A.2 Protocol Description
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