THEORY OF OPERATION

2-1-2. RS422A interface

CN3

RD (+)

RD (–)

CS (+)

CS (–)

RS (–)

RS (+)

SD (–)

SD (+)

 

IC1

CN1

CN9

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R2I

+

 

 

 

 

 

 

 

 

 

 

 

 

 

+

 

 

 

 

 

D2O

A15

A15

 

 

 

 

 

 

 

 

 

 

 

 

R2I

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R1I

+

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

+

 

 

 

 

 

D1O

B15

B15

 

 

 

 

R1I

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

D2EN

A10

A10

 

 

 

 

 

 

 

 

 

 

 

D2O

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

D2I

B12

B12

 

 

 

 

D2O

 

 

 

 

 

 

 

 

 

 

 

 

 

 

D1EN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

D1O

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

D1I

B14

B14

 

 

D1O

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MC34051

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

IC10

Gate array

ERROR

ACK

IC5

CPU

RXD0

TXD0

RXD1

RS422A Interface PCB

Main PCB

Fig. 2-3 RS422A Interface

IC1 operates as the RS422A driver and receiver.

Data flow from host to printer: IC1 receives serial data from the host computer via RD, converts the signal voltage from RS422A level to TTL level, and passes the result to the CPU. The CPU converts the serial data to parallel and stores it into buffer memory.

Data flow from printer to host: The CPU generates data, converts it into serial form, then passes it to IC1. IC1 converts the signal voltage from TTL level to RS422A level, then outputs the result over the SD line.

The CS line is hardware-connected, but the connection is not recognized by software. (The printer does not monitor the signal.)

– 22 –

Page 26
Image 26
Star Micronics TSP400 technical manual 2. RS422A interface