Xon/Xoff - Intermec 4630 User Manual

4630 and 4830 Bar Code Label Printers User's Manual
Note: Do not confuse the DC1 and DC3 status characters in "Standard" protocol with
the XON/XOFF software flow control characters.
When the printer returns Buffer Now Full (<DC3>) status, the currently
received message block is accepted. 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 the entire message block
has been discarded.

XON/XOFF

When you select the XON/XOFF protocol, software and hardware flow control
are concurrently enabled. Software flow control uses the ASCII characters
<DC1> (XON) and <DC3> (XOFF) to start and stop the flow of data from the
host to the printer. Hardware flow control uses pin 20 on the printer's serial
port to indicate "Ready" or "Busy" for data flow control. Status responses
conform to the table on the preceding page except that <DC2> is substituted
for <DC1> and <DC4> is substituted for <DC3>.
Pin 20 reports "Ready" and a <DC1> (XON) is transmitted when the printer
finishes reloading at power-up. It reports "Busy" when the printer's input
buffer fills with 3116 bytes of data. If the host ignores pin 20 and continues to
transmit data, the printer transmits a <DC3> (XOFF) after receiving 15
additional characters. The printer continues to transmit a <DC3> after every
15 characters received if the host continues to transmit data. Data integrity is
not guaranteed if this happens.
Pin 20 becomes "Ready" when the printer has transferred all the data from the
input buffer. If a <DC3> was sent, the printer transmits a <DC1> (XON) and
the host may resume transmission. When the printer is switched to Offline, pin
20 becomes "Busy" and a <DC3> is transmitted. When the printer is switched
to Online (and the input buffer is empty), pin 20 becomes "Ready" and a DC1
is transmitted.
Printer XON/XOFF operation is shown in the following state table:
# of Bytes
Received
Don't Care
3116
3116 + each 15
thereafter
Buffer Empty
Note: Hardware flow control does not work with a multi-drop or modem connection.
B-4
Online/
Offline Pin 20
Offline Busy
Online Busy
Online Busy
Online Ready
Transmit
DC3
DC3
DC1 (if DC3 was sent)