HD-4702_06 Datasheet, PDF (1/8 Pages) Intersil Corporation – CMOS Programmable Bit Rate Generator

®
Data Sheet
August 24, 2006
HD-4702
FN2954.2
CMOS Programmable Bit Rate Generator
The HD-4702 Bit Rate Generator provides the necessary
clock signals for digital data transmission systems, 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 ³ 16 prescaler). A
lower input frequency will result in a proportionally lower
output frequency.
The HD-4702 can provide multi-channel operation with a
minimum of external logic by having the clock frequency CO
and the ³ 8 prescaler outputs Q0, Q1, Q2 available externally.
All signals have a 50% duty cycle except 1800 Baud, which
has less than 0.39% distortion.
The four rate select inputs (S0-S3) select which bit rate is at
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 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, which is easily
achieved with a single 5-position switch.
The HD-4702 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 level on the
CP input after the ECP input goes low. When ECP is high,
selecting the crystal input, CP must be low. A high level on
CP would apply a continuous reset. See Clock Modes and
Initialization below.
Features
• HD-4702 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 EIA RS-404
• One HD-4702 Controls up to Eight Transmission
Channels
• Initialization Circuit Facilitates Diagnostic Fault Isolation
• On-Chip Input Pull-Up Circuit
Ordering Information
PACKAGE
TEMP.
RANGE
(^oC)
PART
NUMBER
PART
PKG.
MARKING NO.
PDIP
-40 to +85 HD3-4702-9
HD3-4702-9 E16.3
PDIP
(Pb-free)
-40 to +85 HD3-4702-9Z* HD3-4702-9Z E16.3
CerDIP
SMD#
-55 to [phone]MEA
F16.3
*Pb-free PDIPs can be used for through hole wave solder
processing only. They are not intended for use in Reflow solder
processing applications.
Truth Table
TRUTH TABLE FOR RATE SELECT INPUTS
(Using 2.4576MHz Crystal)
S3
S2
S1
S0
OUTPUT RATE (Z)
L
L
L
L
MUX Input (IM)
L
L
L
H
MUX Input (IM)
L
L
H
L
50 Baud
L
L
H
H
75 Baud
L
H
L
L
134.5 Baud
L
H
L
H
200 Baud
L
H
H
L
600 Baud
L
H
H
H
2400 Baud
H
L
L
L
9600 Baud
H
L
L
H
4800 Baud
H
L
H
L
1800 Baud
H
L
H
H
1200 Baud
H
H
L
L
2400 Baud
H
H
L
H
300 Baud
H
H
H
L
150 Baud
H
H
H
H
110 Baud
NOTE: 19200 Baud by connecting Q2 to IM.
Pinout
HD-4702 (16 Ld PDIP)
TOP VIEW
Q0 1
Q1 2
Q2 3
E_CP 4
CP 5
O_X 6
I_X 7
GND 8
16 V_CC
15 I_M
14 S0
13 S1
12 S2
11 S3
10 Z
9 CO
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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