The jumpers at J2

Jumpers at J2 are single position jumpers; they can be either installed or disconnected. To change the settigs of these jumpers you must put a jumper plug across the two pins. To disconnect a jumper plug, simply move the plug so that it rests on the left pin only, leaving the right pin open. (All plugs are in this position when the interface is delivered from the factory.)

Table. Function so the jumpers

T2

Connects DM+ and DM- through a 120 ohm resistor.

Tl

Connects RD+ and RD- through a 120 ohm resistor.

 

Connects RD- to pin 9

E L

Connects RD+topin 10

D M

Connects DM- to pin 23

DM+

Connects DM+ to pin 24

SD+

Connects SD+topin 12

TR+

Connects TR+ to pin 25

TR-

Connects TR-to pin 13

Communications Protocols

To achieve the maximum printing speed, the computer should send characters to the printer faster than the printer can print them. This ensures that the printer has to stop and wait for more information. But if you continuously send information to the printer faster than it can print, sooner or later the printer’s buffer will overflow and information will be lost. A communications protocol keeps the computer from sending more information than the printer can

handle. *

The GQ-35CN7's serial interface can use three different kinds of communications protocols These are described in detail below.

The ETX/ACK protocol

The ETX/ACK protocol uses a special pair of control codes, ETX (ASCII 3) and ACK (ASCII 6). The system is very simple: whenever the GQ-3500 gets an ETX out of its input buffer it sends an ACK back to the computer. When the computer receives the ACK it knows it is safe to send more information to the printer without fear of overflowing the buffer.

8

Serial Interface