Allen Bradley1771-DAASCII I/O Module, RS-232-C and 20 mA Current Loop, 1.5K Word Buffer, 1771 I/O

Product Description

What this part is

Allen-Bradley 1771-DA ASCII I/O module, Series B. Product Type: ASCII serial interface module for the 1771 I/O platform. Function: moves character data between an ASCII device and a programmable controller data table on the I/O scan. Buffer Memory: 1.5K words, 3K bytes. Backplane Current: 1.3 A. Mounting Type: 1771 I/O chassis slot. Unit Quantity: 1 Pc.

Decoding the designation

1771 — the Allen-Bradley 1771 I/O platform, the rack-based I/O family served by PLC-2, PLC-3 and PLC-5 processors.

DA — the ASCII I/O module within that platform, the serial-character interface as distinct from the 1771-DB BASIC module, which runs a user program.

Series B — the second hardware revision of the module.

Communication data

Communication Standard: RS-232-C, 20 mA current loop and Allen-Bradley long line. Baud Rates: 110, 300, 600, 1200, 2400, 4800 and 9600, user-selectable. Buffer Memory: 1.5K words, 3K bytes. Backplane Current: 1.3 A.

RS-232-C Receiver: 3 to 25 V DC input, 3 to 7 kΩ input impedance. RS-232-C Transmitter: 5 to 15 V DC for the space state, −5 to −15 V DC for the mark state.

Current Loop Receiver: passive circuit, 4 to 20 mA input current range, 1.5 to 2.05 V DC nominal, 5 V DC reverse voltage limit.

What these specs mean in practice

Communication Standard: RS-232-C, 20 mA current loop and long line on one module. Three physical layers on a single catalogue number covers a short desk-side terminal run, a noisy long factory run on current loop, and the Allen-Bradley proprietary long-line distance.

Buffer Memory: 1.5K words. The module holds the character stream in its own memory and hands complete blocks to the processor, so the ladder scan is decoupled from the serial device’s timing.

Baud Rates: 110 to 9600. The low end reaches teletype-era printers and weigh heads still in service on legacy lines; 9600 suits terminals and barcode readers.

Backplane Current: 1.3 A. This is a substantial share of a 1771 chassis budget and is the figure that decides how many intelligent modules a 1771-P series supply will carry.

Mounting data

Mounting Type: single slot in a 1771 I/O chassis. Terminations: removable field wiring arm. Controller Platform: PLC-2, PLC-3 and PLC-5 processors using the 1771 I/O structure. Data Transfer: block transfer read and write.

Quantity and configuration

Unit Quantity: 1 Pc. One ASCII I/O module.

Interchange guidance

Manufacturer Status: discontinued. Part Number: 1771-DA. MPN Variants: 1771DA, 1771 DA. The 1771-DB BASIC module occupies the same slot and the same serial world but runs a user BASIC program, so it is a related module rather than an equal. Reference documentation: Rockwell publication 1771-UM513, ASCII I/O Module User Manual.