dm9370 Fairchild Semiconductor, dm9370 Datasheet - Page 2

• Manufacturer Part Number: dm9370
• Description: 7-segment Decoder/driver/latch With Open-collector Outputs
• Manufacturer: Fairchild Semiconductor

www.fairchildsemi.com
Truth Table
*The RBI will blank the display only if binary zero is stored in the latches.
**RBO used as an input overdrives all other input conditions.
H
L
X
Functional Description
The DM9370 has active LOW outputs capable of sinking in
excess of 25 mA which allows it to drive a wide variety of 7-
segment incandescent displays directly. It may also be
used to drive common anode LED displays, multiplexed or
directly with the aid of suitable current limiting resistors.
This device accepts a 4-bit binary code and produces out-
put drive to the appropriate segments of the 7-segment dis-
play. It has a hexadecimal decode format which produces
numeric codes “0” through “9” and alpha codes “A” through
“F” using upper and lower case fonts.
Latches on the four data inputs are controlled by an active
LOW latch enable LE. When the LE is LOW, the state of
the outputs is determined by the input data. When the LE
goes HIGH, the last data present at the inputs is stored in
the latches and the outputs remain stable. The LE pulse
width necessary to accept and store data is typically 30 ns
which allows data to be strobed into the DM9370 at normal
TTL speeds. This feature means that data can be routed
directly from high speed counters and frequency dividers
into the display without slowing down the system clock or
providing intermediate data storage.
The latch/decoder combination is a simple system which
drives incandescent displays with multiplexed data inputs
from MOS time clocks, DVMs, calculator chips, etc. Data
inputs are multiplexed while the displays are in static mode.
This lowers component and insertion costs since several
circuits—seven diodes per display, strobe drivers, a sepa-
rate display voltage source, and clock failure detect cir-
LOW Voltage Level
HIGH Voltage Level
Immaterial
2
cuits—traditionally found in incandescent multiplexed
display systems are eliminated. It also allows low strobing
rates to be used without display flicker.
Another DM9370 feature is the reduced loading on the
data inputs when the Latch Enable is HIGH (only 10 A
typ). This allows many DM9370s to be driven from a MOS
device in multiplex mode without the need for drivers on
the data lines. The DM9370 also provides automatic blank-
ing of the leading and/or trailing-edge zeroes in a multidigit
decimal number, resulting in an easily readable decimal
display conforming to normal writing practice. In an 8-digit
mixed integer fraction decimal representation, using the
automatic blanking capability, 0060.0300 would be dis-
played as 60.03. Leading-edge zero suppression is
obtained by connecting the Ripple Blanking Output (RBO)
of a decoder to the Ripple Blanking Input (RBI) of the next
lower stage device. The most significant decoder stage
should have the RBI input grounded; and since suppres-
sion of the least significant integer zero in a number is not
usually desired, the RBI input of this decoder stage should
be left open. A similar procedure for the fractional part of a
display will provide automatic suppression of trailing-edge
zeroes. The RBO terminal of the decoder can be OR-tied
with a modulating signal via an isolating buffer to achieve
pulse duration intensity modulation. A suitable signal can
be generated for this purpose by forming a variable fre-
quency multivibrator with a cross coupled pair of TTL or
DTL gates.