Epson Serial Interface GQ-3500 User Manual page 10

The GQ-3500 has a buffer that will hold up to 102 characters,
including the ETX code at the end of the group. The computer can
send the first group of characters and then stop until the first ACK is
received. From then on,every time an ACK is received, another
group of characters can be sent.
DlP switch 5-2 controls ETX/ACK protocol. If DIP switch 5-2
iS Off, the GQ-35OO is ignored the ETX code.
The DCl/DC3 or XON/XOFF protocol
The DC1/DC3 protocol also uses a special pair of control codes,
DCl (AscII 17 decimal, also knwon as XON) and DC3 ( ASCII 19)
decimal, also known as XOFF) This communications protocol is
selected by turning DIP switch 5-1 on.
In this protocol the printer sends a DC3 to the computer to suspend
data entry under the following conditions
1. when the input buffer becomes nearly full (within 128 bytes)
2 When the printer goes offline (by pressing the ONLlNE button)
3. When the printer runs out of paper
4. When the printer runs out of toner
5. When an errror is detected.
when the computer receives the DC3 signal it must stop within
128 characters) sending information until the printer sends a DCl signal
to say that there is more room in the buffer. The printer sends the DCl
signal when the buffer has room for 255 characters
If DIP switch 5-4 is on, the printer will send an additional DC3
after each additional character it receives after it sends the first DC3.
This is called the multiple XOFF function.
The printer ready protocol
The printer ready protocol is a hardware protocol because it uses
one of the wires in cable connecting the computer and printer to tell
the computer where , the printer is ready to accept information. This
communications potocol is selected by turning DIP switch 5-3 on.
serial Interface
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