Rockwell Automation 1771-DA,D17716.5.13 U MNL 1771-DA ASCII I/O MODULE - Manual (Page 141)

Function of Control/Status Bits
Chapter 6
6Ć6
Bit: IW1(14)
Function: Parity
Description: Reset it to zero (default) for odd parity. Set it for even
parity. Ignore it if you do not enable parity, IW1(15)=0.
Bit: IW1(15)
Function: Parity Enable
Description: Reset it to zero (default) when your ASCII device does not
generate a parity bit. Set it when your ASCII device generates a parity bit
for each character. See IW1(14).
Bit: IW1(16)
Function: Stop Bits
Description: Reset it to zero (default) when your ASCII device generates
only one stop bit per character. Set it when your ASCII device generates
two consecutive stop bits per character. Refer to chapter 2, Figure 2.12.
Bit: IW1(17)
Function: ACK/NAK
Description: Reset it to zero (default) when the ASCII device does not
require an ACK/NAK from the module to complete the transmission. Set
it when an acknowledgment of no error per character string (ACK), or
error found in the string (NAK), is required by the ASCII device to
complete the transmission. The ASCII module does not require an
ACK/NAK to complete its transmission.
Initialization Word Two, IW2
Bit: IW2(00-13)
Function: Number of ASCII Characters Per String (read, only)
Description: In data mode, enter a 3-digit BCD number for the maximum
number of ASCII characters per string generated by your ASCII device.
Count header and trailing characters, not removed by the module, as part
of the string length.
In report generation mode, enter a 3-digit BCD number for the number of
characters generated by your longest message line. Normally, the
end-of-string delimiter is not counted as a character in the string (data
mode or report generation mode). Count the end-of-string delimiter as a
character in your string only if you send the end-of-string delimiter to the
processor by setting IW3(04).