Levels of Implementation

 

 

Table A-1. EIA-232-D Interconnections (Continued)

 

 

 

 

 

 

Pin

Signal

 

 

 

Number

Mnemonic

Signal Name and Description

 

 

 

 

 

 

 

22

RI

RING INDICATOR. Output from the modem to the terminal;

 

 

 

 

indicates to the terminal that an incoming call is present. The

 

 

 

 

terminal causes the modem to answer the phone by carrying

 

 

 

 

DTR true while RI is active.

 

 

 

 

 

 

 

23

 

Not used.

 

 

 

 

 

 

 

24

TxC

TRANSMIT CLOCK (DTE). Input to modem from terminal;

 

 

 

 

same function as TxC on pin 15.

 

 

 

 

 

 

 

25

BSY

BUSY. Input to modem from terminal. A positive EIA signal

 

 

 

 

applied to this pin causes the modem to go off-hook and make

 

 

 

 

the associated phone busy.

 

 

 

 

 

 

Notes:

1.A high EIA-232-D signal level is +3 to +15 volts. A low level is -3 to -15 volts. Connecting units in parallel may produce out-of-range voltages and is contrary to specifications.

2.The EIA-232-D interface is intended to connect a terminal to a modem. When computers are connected without modems, one must be configured as a modem and the other as a terminal.

Levels of Implementation

There are several levels of conformance that may be appropriate for typical EIA-232-D interconnections. The bare minimum requirement is the two data lines and a ground. The full implementation of EIA-232-D requires 12 lines; it accommodates:

Automatic dialing

Automatic answering

Synchronous transmission

A middle-of-the-road approach is illustrated in Figure A-1.

A-3

A

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Motorola MVME177 manual Levels of Implementation, Pin, Number Mnemonic Signal Name and Description