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DR300 Operator Manual
78
XON / XOFF
X-on/X-off flow control must be used whenever hardware (Ready/Busy) flow control is
not available or desirable. Instead of a voltage going high/low at pin 20, control
characters representing “Printer Ready” (X-on = 11 hexadecimal) or “Printer Busy” (X-
off = 13 hexadecimal) are transmitted by the printer on pin 2 (Transmit Data) to the host.
In order for this method of flow to function correctly, the host must be capable of
supporting it. X-on/X-off operates in a manner similar to the function of pin 20 (DTR)
as previously explained. When the printer is first powered on and goes on-line, an X-on
is sent out. In the Single Job Buffer mode, when the printer receives a viable job, it
transmits an X-off and begins printing. When it is done printing, it transmits an X-on. In
the Multi Job Buffer mode, the printer sends an X-off when the “Buffer Near Full” is
reached and an X-On when the data level of the buffer drops below the “Buffer
Available” mark. When the printer is taken offline manually, it transmits an X-Off
indicating it cannot accept data. When it is placed back online manually, it sends an X-
On, indicating it is again available for receipt of data. If an error occurs during printing
(paper out, ribbon out), the printer sends nothing in the Single Job Buffer mode since the
last character transmitted was an X-Off. When the error is cleared and the printer
resumes printing, no X-On is sent until the current job is completed and the printer is
once again ready to receive the next job. If it is in the Multi Job Buffer mode, it sends an
X-Off as soon as an error condition is detected. When the error is cleared and the printer
is placed back online, it transmits an X-On indicating it is again ready to accept data.
Data stream (ESC + “A” ~ ESC + “Z”) from host might not be fully received by printer
under the following conditions:
• Printer is in printing process during Single Job Buffer Mode
• Printer is engaged with error condition
1 : Cable connection
Host Printer
FG 1 FG
RD 2 SD
SD 3 RD
SG 7 SG
• Some host needs looping of RS and CS at host side to keep signal High.
Chapter 10 - Serial Interface