Full Duplex Tty/Eia Module-To-Current Loop Device Interface; Full Duplex Tty/Eia Module-To-Eia Device Interface - Texas Instruments 990 Maintenance Manual

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Write Request (WR Q). Logic 1 active.
Read Request (RRQ). Logic 1 active.
Data Carrier Detect ( DCD). Logic 1 active.
Data Set Ready ( DSR). Logic 1 active.
Interrupt (INT). Logic 1 active.
The CRUD AT AIN signals should be recognizable as the outputs of the multiplexer described in
paragraph 4.2.21.
4.3.1.7 CRUINT-. CRUINT- is the logical OR of Read Request, Write Request, and New Status
and is always active (low) when bit F of the output word is set.
4.3.2 FULL DUPLEX TTY/EIA MODULE-TO-CURRENT LOOP DEVICE INTERFACE. The
current loop interface consists of two pairs of lines. TTYHX and TTYLX from the transmit
loop, and TTYHR and TTYLR from the receive loop. A closed-loop current of 20 mA is defined
as a "marking" condition, or logic 1. Any break in this circulating current is sensed as a "break"
condition, or logic 0.
4.3.3 FULL DUPLEX TTY/EIA MODULE-TO-EIA DEVICE INTERFACE.
4.3.3.1 Reverse Channel Transmit (RCTE). Reverse Channel Transmit is used only when the
module interfaces with a Bell 202 (C or D) data set or its equivalent. RCTE directs the data set
to turn on/off the reverse channel carrier.
4.3.3.2 Data Terminal Ready (DTRE). Data Terminal Ready indicates to the peripheral device
that the computer is ready to transmit or receive data. When the peripheral device is equipped
for automatic answering of incoming calls, the off condition of DTRE prevents the data set from
answering calls.
4.3.3.3 Request To Send (RTSE). Request To Send establishes the transmit condition for a Bell
103 F data set. RTSE simulates Data Carrier Detect for direct interface to the terminal. Request
To Send is not used with a Bell 103A data set.
4.3.3.4 Transmitted Data (XMTDE). Transmitted Data is the serial data from the computer for
the device.
4.3.3.5 Pseudo Clear To Send (PCTS). Pseudo Clear To Send is high whenever the module's
power is active and provides a simulated Clear To Send signal to the peripheral.
4.3.3.6 Pseudo Data Carrier Detect (PDCD). Pseudo Data Carrier Detect is high whenever the
module's power is active and provides a simulated Data Carrier Detect to the peripheral.
4.3.3.7 Received Data (RCVDE). Received data is the serial data from the device to be transmitted
to the computer.
4.3.3.8 Data Carrier Detect (DCDE). Data Carrier Detect, when high, indicates that the periph-
eral has detected a carrier. When directly interfaced to the peripheral, DCDE reflects the Request
To Send signal.
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Digital Systems Division