22
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.
WAT REGISTERS
MSB LSB
D(y)
Number of data words to
transfer (hex value)
Read/Write
Remote
Remote
Protocol
Header #1
D(y+1)
Remote Register/Device Prefix
(One ASCII Number or letter)
Header #2
D(y+2)
Remote Head Address
(0-1999 decimal)
Header #3
D(y+3)
1
st
Data Word
Data #1
D(y+4)
2
nd
Data Word
Data #2
D(y+x)
(x) Data Word
(where x = 16 (10 hex) maximum)
Data #x
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.
D(y)
WAT Header Address#1
b0-3 Remote Protocol No.
b4-7 Remote Read/Write bit
b8-15 Number of words
b0
b15
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.
