Star Tech Journal

6
STAR*TECH JOURNAL/APRIL 1983
SEGA ELECTRONICS'
ROM LINE (PART 7)
Continuing our ROM LINE
series on integrated circuits,
this issue we will expand on
those devices covered previ-
ously, differentiate between
TTL/LS and CMOS logic,
discuss handling techniques and
look at some common applica-
tions. As we mentioned last
time, the most basic of digital
ICs are the logic gates AND/
NAND, OR/NOR, EXCLU-
SIVE OR/EXCLUSIVE NOR,
the YES ( or BUFFER) and the
NOT ( or INVERTER). These
gates are often grouped together,
several on a single chip, and
comprise the more complex I Cs.
TTL ( or Transistor to Tran-
sistor Logic) at present has the
widest application in the video
games industry and is the most
diversified IC family. Typically,
a TTL device can be recognized
by a 74-preface designation(i.e.
74154). LS (or Low-power
Schottky) is functionally identi-
cal to TTL, but has superior
speed, temperature parameters
and consumes an average of
80% less power. An LS logic
device is differentiated by an
LS in its designator (i.e.
74LS131). Power supply re-
quirements should be kept
regulated within the 4. 7 5 to
5.25vdc range. Also keep in
mind that digital is two-state
logic and inputs should never
exceed supply(5.25vdc) or fall
below ground (Ovdc). A quick
tip on troubleshooting digital
- outputs found to be floating
(held somewhere midway
between 0-Svdc) are always
suspect. Now, on to some
specific chips . . .
The QUAD NAND gate,
7400/74LSOO is a 14-pin IC
that has wide use both as a
convenient packaging of 4
NAND gates on a single chip,
and as a way to consolidate
components for space consider-
ations, ( for example, on the
SPACE TACTICS Logic board,
IC 148 is configured as a single
NAND and a single OR).
Pictured below is an internal
configuration of the 7 400/
74LSOO, and our IC 148
arrangement.
Vee ( +5 VDC)
9
2
3
8
4
Having analyzed a few repre-
sentative TTL devices and their
applications, let's tum now to a
brief discussion ofMOS/CMOS.
MOS stands for Metal Oxide
Silicon/or Semiconductor. By
and large you will be concerned
with Complimentary MOS or
CMOS. These I Cs can contain
Vee (+5 VOC)
more functions per chip than
14
TTL/LS and consume very little
power operating over a supply
range of +3 to 15vdc. CMOS
chips are multiple stratis devices
( similar to other formats) with
the unique addition of a silicon
dioxide film separating the input
port from the other junctions.
4
It's this thin, glassy layer that
enables the chip to impose very
low loads on the input signal
source, while at the same time
standing as this chip-type's
"Achilles Heel". Susceptibility
· to static damage requires care-
ful handling techniques that
include exclusive use of DC
powered irons or well isolated,
IC 148
controlled output soldering
stations, and storage only in
The 7410/74LS10 is a 14- conductive foam or pins down
pin, Triple 3-input NAND gate on aluminum foil. Ground dif-
generally used for decoder or ferentials should be strictly
observed.
enable control functions:
Next month: A TTL review.