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3.6.2 Information in the WAT Header
The instructions read by the modem from the WAT header are in the form shown in
the two figures below. It is the responsibility of the PLC program to transfer the
correct information into these registers before requesting the transaction.
MSB
D(y)
Number of data words to
transfer (hex value)
D(y+1)
D(y+2)
D(y+3)
D(y+4)
D(y+x)
(where x = 16 (10 hex) maximum)
Where D(y) = Head Address of the WAT Message data area specified with the
AT%WAT command.
The contents of Header #1 are further described below.
b15
D(y)
Where D(y) Is the first WAT header address.
Bits 15 to 8 - The number of words to Transmit or Receive are limited to 16 (1 to 10h)
Bits 7 to 4 - Read/Write Remote, 0 = Read from Remote and 1 = Write to Remote.
Bits 3 to 0 - Remote Protocol Number refers to the remote PLC type, e.g. 1 = AnS PLC,
3 = FX PLC.
WAT REGISTERS
Read/Write
Remote
Remote Register/Device Prefix
(One ASCII Number or letter)
Remote Head Address
(0-1999 decimal)
st
1
Data Word
nd
2
Data Word
(x) Data Word
22
LSB
Remote
Header #1
Protocol
Header #2
Header #3
Data #1
Data #2
Data #x
b0
WAT Header Address#1
b0-3 Remote Protocol No.
b4-7 Remote Read/Write bit
b8-15 Number of words
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