Ack character, Nak character – Rockwell Automation 2755 Enhanced Decoder Series B User Manual
Page 166
12–4
Configuration: Host Communications
Publication 2755-833
ACK Character
Field Type Options
Edit ASCII
0 through 255
255 = None
Defines an Acknowledge (ACK) character for ACK/NAK protocol.
The first time the decoder is started, the default is None, which
means an ACK character is not defined. From then on, the default is
determined at restart by the contents of storage memory.
①
The ACK character is sent by the host to acknowledge receipt of a
message. The decoder holds the last transmitted message until an
ACK is returned to the decoder. Any command the decoder receives
from the host is also interpreted as an ACK character.
You must define ACK and NAK characters to enable ACK/NAK
protocol with the host. ACK/NAK protocol only applies to bar
code data sent to the host. It is typically used with the
transmission check to provide error detection. You can also use
ACK/NAK protocol to provide flow control.
NAK Character
Field Type Options
Edit ASCII
0 through 255
255 = None
Defines a Negative Acknowledge (NAK) character for ACK/NAK
protocol. The first time the decoder is started, the default is None,
which means a NAK character is not defined. From then on, the
default is determined at restart by the contents of storage memory.
①
The NAK character is sent by the host when a message is not
received properly and prompts the decoder to retransmit the last
message up to three times.
① If any of the characters below are used as single character commands (ACK/NAK or Start/
Characters), then the escape sequence (ESC=!) must be used with all two character comm
start with that character.
A B C D H I M N O P R S T
If the single character commands do not use these uppercase characters, you do not have to
start command sequence. For example, if N is used as the NAK command, then it would b
impossible to send the NR command without preceding it with the ESC=! start command s
If n is used instead, then no start command sequence would be necessary to send an NR co
Therefore, we recommend using only lowercase letters for single character command
Refer to Chapter 15 for additional information.