Series 700
Maintenance Manual
Model 750
Rev H
Page 23
Serial Interface Specifications
The XON/XOFF Protocol
The RS-232 serial interface communicates using hardware and XON/XOFF flow control.
Flow control helps to ensure that the computer does not send information to the printer
faster than it can print.
The XON/XOFF protocol is a popular data communications protocol. When the printer’s
buffer is approximately 50 percent full, it sends the ASCII code XOFF (13 Hex) to the
computer to tell it to stop sending data. When there is again room (that is, space for
approximately 30 percent more characters in the buffer), the printer sends the ASCII
code XON (11 Hex) to the computer to tell it to resume sending data. (XON is also
known as DC1; XOFF is synonymous with DC3.) If the computer does not stop sending
data after it receives an XOFF, the data that overflows the buffer will be lost and the
printer will halt.
The printer will send an XON code when it goes on-line to get things started.
It will send an XOFF code to stop the computer from sending information
if the input buffer is approximately 50 percent full.
Board Close-ups and Physical Connections
The following insert pages are as follows:
•
Model 750 Wiring Schematic
•
Power Board Connections Schematic
•
Connector Board Connections Schematic
•
Controller Board Connections Schematic
Figure 7 Model 750 Wiring Schematic
Figure 8 Power Board Connections Schematic
Figure 9 Connector Board Connections Schematic
Figure 10 Controller Board Connections Schemaitc
