Rockwell Automation 1771-DA,D17716.5.13 U MNL 1771-DA ASCII I/O MODULE - Manual (Page 70)

Choosing Module Features
Chapter 3
3Ć28
Parity
Your ASCII device generates either odd, even, or no parity bit with each
character (Figure 2.12). Use the default value (no parity) if this
information is not available. Set bits IW1(14,15) accordingly.
Figure 2.12
Serial Data on RSĆ232ĆC Line
Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7 Bit 8
Optional
Parity Bit, Optional
Stop Bits
Optional Start Bit Last Stop Bit
or Marker
11831
Number of Stop Bits
Your ASCII device generates either one or two stop bits (Figure 2.12).
Use the default value (one stop bit) if this information is not available.
Set bit IW1(16) accordingly.
ACK/NAK
Some ASCII devices require an ACK/NAK response from the ASCII
module. An acknowledgment of no errors found in a string (ACK) or
acknowledgment of an error found in the string (NAK) is required by
some ASCII devices in order to complete its transmission. Other ASCII
devices do not require acknowledgment.
The ASCII module does not require an ACK/NAK to complete its
transmission. Most ASCII devices do not require transmission
acknowledgment. Set bit IW1(17) accordingly.