Motorola MVME187 User Manual

Levels of Implementation

E-3

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 

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.