Rockwell Automation 1771-DA,D17716.5.13 U MNL 1771-DA ASCII I/O MODULE - Manual (Page 146)

Function of Control/Status Bits
Chapter 6
6Ć11
module detects that IW3(10-16) is equal to IW4(10-16), it will not operate
due to an initialization error.
Bit: IW3(17)
Function: Enables End-of-String Delimiter
Description: Reset it to zero (default) to enable the end-of-string
delimiter that you selected in IW3(10-16). Set it when not using an
end-of-string delimiter. When set, the module will transfer your data
string when its input buffer receives the next character beyond your
selected string length.
When the end-of-string delimiter is not enabled (IW3(17)=1), the null
character, CTRL 0, is treated as an end-of-string delimiter even though
you have not selected it.
Initialization Word Four, IW4
Bits: IW4(00-03)
Function: Removes Header Characters
Description: Select the number of header characters, up to 15, preceding
the data string that you want the module to remove when it sends data to
the PC processor data table. If no bits are set, the module defaults to zero
(no header characters are removed).
Set bit 00-03 to the binary code for the number of header characters that
you want the module to remove.
Bits: IW4(04-07)
Function: Removes Trailing Characters
Description: Select the number of trailing characters, up to 15, following
the data string that you want the module to remove when it sends data to
the PC processor data table. This number does not include the
end-of-string delimiter unless you are sending the end-of-string delimiter
to the processor. If no bits are set, the module defaults to zero (no trailing
characters are removed).
Set bits 04-07 to the binary code for the number of trailing characters that
you want the module to remove.
Bits: IW4(10-16)
Function: BCD Delimiter/Removes Fill Character
Description: BCD Delimiter (Report Generation Mode)