1

June 1998

HD-4702/883

CMOS Programmable Bit Rate Generator

Features

• This Circuit is Processed in Accordance to MIL-STD-883

and is Fully Conformant Under the Provisions of

Paragraph 1. 2. 1.

• HD-4702/883 Provides 13 Commonly Used Bit Rates

• Uses a 2.4576MHz Crystal/Input for Standard

Frequency Output (16 Times Bit Rate)

• Low Power Dissipation

• Conforms to ElA RS-404

• One HD-4702/883 Controls up to Eight Transmission

Channels

• Initialization Circuit Facilitates Diagnostic Fault

Isolation

• On-Chip Input Pull-Up Circuit

Description

The

HD-4702/883

Bit

Rate

Generator

provides

the

necessary clock signals for digital data transmission sys-

tems, such as a UART. It generates 13 commonly used bit

rates using an on-chip crystal oscillator or an external input.

For conventional operation generating 16 output clock

pulses per bit period, the input clock frequency must be

2.4576MHz (i.e., 9600 Baud x 16 x 16, since there is an

internal

÷ 16 prescaler). A lower input frequency will result in

a proportionally lower output frequency.

The HD-4702/883 can provide multi-channel operation with

a minimum of external logic by having the clock frequency

externally. All signals have a 50% duty cycle except 1800

Baud, which has less than 0.39% distortion.

the output (Z). See Truth Table for Rate Select Inputs for

select code and output bit rate. Two of the 16 select codes

for the HD-4702/883 do not select an internally generated

frequency, but select an input into which the user can feed

either a different frequency, or a static level (High or Low) to

generate “ZERO BAUD”.

The bit rates most commonly used in modern data terminals

(110,150, 300,1200, 2400 Baud) require that no more than

one input be grounded for the HD-4702/883, which is easily

achieved with a single 5-position switch.

The

HD-4702/883

has

an

initialization

circuit

which

generates a master reset for the scan counter. This signal is

derived from a digital differentiator that senses the first high

Modes and Initialization below.

Pinout

HD-4702/883 (CERDIP)

TOP VIEW

Ordering Information

PART

NUMBER

TEMPERATURE

PACKAGE

PKG. NO.

HD1-4702/883

-55 to 125

CERDIP

F16.3

14

15

16

9

13

12

11

10

1

2

3

4

5

7

6

8

GND

Z

File Number

2955.2

CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.

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