Xon/Xoff Protocol (Software And Hardware Flow Control) - Intermec EasyCoder 4420 User Manual

XON/XOFF Protocol (Software and Hardware Flow Control)

EasyCoder 4420 and 4440 Bar Code Label Printer User's Manual
Note: Do not confuse the Buffer now full <DC3> status with the
XON/XOFF characters <DC1> and <DC3>.
When the printer returns Buffer now full (<DC3>) status, it accepts the
currently received message block. At this time, the printer can accept short
messages to allow parsing of immediate commands such as Reset (<DLE>)
or Cancel batch printing (<EM>). However, if the printer responds with a
<GS> to any message block, the buffer is already full and it discards the
entire message block.
XON/XOFF protocol uses the ASCII characters <DC1> (XON) and
<DC3> (XOFF) to start and stop the flow of data from the host to the
printer. The printer does not restrict the message length for XON/XOFF
protocol. That is, the printer processes information as it is being
downloaded and stops when there is no more information.
<STX> and <ETX> are optional characters. However, if you send an STX,
the printer ignores all other characters until you send an ETX.
Intermec provides two versions of the XON/XOFF protocol. The
Intermec version of XON/XOFF has the printer respond to each message
with its current status. The other version conforms to generally accepted
industry standards, which include no end-of-message response being sent
to the host other than XOFF. In addition, a DC3 is sent to the host if the
printer is offline or if media fault occurs. An XON is sent on power up.
Since the printer uses DC1 and DC3 for data flow control, the printer
status characters are different from those of the Standard Protocol.
XON/XOFF Protocol Printer Status Conditions
Printer Status Character
Buffer already full GS
Ribbon fault US
No label stock EM
Printhead hot SI
Buffer now full DC4
Label at strip pin FS
Label skipping DC2
Printing DC2
Ready DC2
If the host ignores the printer sending an XOFF, the printer resends an
XOFF after receiving every 15 characters from the host. In the case of
transmission error, the printer discards the characters with the error and
keeps the rest of the message block.
Appendix C — Communications Reference
95