7 Detailed Description

7.1 Overview

The AM26C32 is a quadruple differential line receiver that meets the necessary requirements for NSI TIA/

EIA-422-B, TIA/EIA-423-B, and ITU Recommendation V.10 and V.11. This device allows a low power or low

voltage MCU to interface with heavy machinery, subsystems and other devices through long wires of up to

1000m, giving any design a reliable and easy to use connection. As any RS422 interface, the AM26C32 works in

a differential voltage range, which enables very good signal integrity.

7.2 Functional Block Diagram

Input

VCC

EQUIVALENT OF A OR B INPUT

TYPICAL OF ALL OUTPUTS

Output

VCC

VCC

1.7 k

Ω

NOM

GND

GND

1.7 k

Ω

NOM

17 k

Ω

NOM

288 k

Ω

NOM

VCC (A inputs)

or

GND (B inputs)

Input

GND

EQUIVALENT OF G OR G INPUT

7.3 Feature Description

7.3.1 ±7-V Common-Mode Range With ±200-mV Sensitivity

For a common-mode voltage varying from -7V to 7V, the input voltage is acceptable in low ranges greater than

200 mV as a standard.

7.3.2 Input Fail-Safe Circuitry

RS-485 specifies that the receiver output state should be logic high for differential input voltages of VAB ≥ +200

mV and logic low for VAB ≤ –200 mV. For input voltages in between these limits, a receiver’s output state is

not defined and can randomly assume high or low. Removing the uncertainty of random output states, modern

transceiver designs include internal biasing circuits that put the receiver output into a defined state (typically

high) in the absence of a valid input signal.

A loss of input signal can be caused by an pen circuit caused by a wire break or the unintentional disconnection

of a transceiver from the bus. The AM26C32 has an internal circuit that ensures functionality during an idle bus.

7.3.3 Active-High and Active-Low

The device can be configure using the G and G logic inputs to select receiver output. The high voltage or logic 1

on the G pin, allows the device to operate on an active-high and having a low voltage or logic 0 on the G enables

active low operation. These are simply a way to configure the logic to match that of the receiving or transmitting

controller or microprocessor.

7.3.4 Operates from a Single 5-V Supply

Both the logic and receivers operate from a single 5-V rail, making designs much more simple. The line drivers

and receivers can operate off the same rail as the host controller or a similar low voltage supply, thus simplifying

power structure.

AM26C32, AM26C32C, AM26C32M, AM26C32I

SLLS104M – DECEMBER 1990 – REVISED OCTOBER 2023

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