HD-4702/883
June 1998
CMOS Programmable Bit Rate Generator
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
梅
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
C
O
and the
梅
8 prescaler outputs Q
0
, Q
1
, Q
2
available
externally. All signals have a 50% duty cycle except 1800
Baud, which has less than 0.39% distortion.
The four rate select inputs (S
0
-S
3
) 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-4702/883 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 鈥淶ERO BAUD鈥?
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 鏗乺st high
level on the C
P
input after the E
CP
input goes low. When
E
CP
is high, selecting the crystal input, C
P
must be low. A
high level on C
P
would apply a continuous reset. See Clock
Modes and Initialization below.
Features
鈥?This Circuit is Processed in Accordance to MIL-STD-883
and is Fully Conformant Under the Provisions of
Paragraph 1. 2. 1.
鈥?HD-4702/883 Provides 13 Commonly Used Bit Rates
鈥?Uses a 2.4576MHz Crystal/Input for Standard
Frequency Output (16 Times Bit Rate)
鈥?Low Power Dissipation
鈥?Conforms to ElA RS-404
鈥?One HD-4702/883 Controls up to Eight Transmission
Channels
鈥?Initialization Circuit Facilitates Diagnostic Fault
Isolation
鈥?On-Chip Input Pull-Up Circuit
Ordering Information
PART
NUMBER
HD1-4702/883
TEMPERATURE
RANGE (
o
C)
-55 to 125
PACKAGE
CERDIP
PKG. NO.
F16.3
Pinout
HD-4702/883 (CERDIP)
TOP VIEW
Q
0
Q
1
Q
2
E
CP
C
P
O
X
I
X
GND
1
2
3
4
5
6
7
8
16 V
CC
15 I
M
14 S
0
13 S
1
12 S
2
11 S
3
10 Z
9 C
O
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
http://www.intersil.com or 407-727-9207
|
Copyright
漏
Intersil Corporation 1999
File Number
2955.2
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