6.
-6V
"Wire-up" the circuit in figure
2 on the breadboard. Before
1500
T
- 6V
I
I
I
I rL .o Ia
L1
__
IN91-4
j
Figure 1
B
X
0
0
0
9. Set S1 to the low (l) position
and S2 to the high position . The
lamp should remain lit.
When S2 is in the high (H) posi-
tion, a logic 1 is applied to input B.
The output has remained at a
logic 1. Again the operating
condition is shown in section 2 of
figure 6-3. The student should
state this logic condition on the
third row of the Truth Table.
Table for figures 1 & 2
-6V
-6V
r
I
I
~
~-r~-M.--.-------ox
-l- _:
7. Apply power, - 6V only. The
lamp should not light.
When both inputs are at a logic 0,
diodes 01 and 02 are both
reverse-biased and the output is
at a lofic 0. The first row of the
Truth Table states this operating
condition . The operating condi-
tion is illustrated in section 1 of
figure 6-3.
8. Set S1 to the high (H) posi-
tion . The lamp should light. When
S1 is in the high position , input A
is at a logic 1. This operating
condition is shown in section 2 of
figure 6-3 . The student should
state this operating condition on
the second row of the Truth
Table.
Truth Table
A
applying power, set switches S1
and S2 to the low (l) position .
Output
1
10 . Set S1 to the high (H)
position . The lamp should remain
lit. Both inputs are now at a logic 1
and the output is also at a logic 1.
Section 3 of figure 6-3 illustrates
this, operating condition . The
student should state this logic
condition in the bottom row of the
Truth Table.
When completed, the Truth Table
should be the same as the one
shown in figure 6-2.
The circuit has performed the
operation OR .
Figure 2
state this logic condition in the
third row of the Truth Table.
5 . Set S1 to the high (H)
position . The lamp should
extinguish .
Both diodes are now zero-biased
and the output has risen to a high
level or logic 1. This operating
condition is illustrated in figure 6-
5, section 3.
The stu dent should state the logic
condition in the bottom row of the
Truth Table. When completed,
the Truth Table should be the
same as the one shown in figure
6-4 .
This circuit has performed the
operation AND .
PLAY METER, May 1, 1981
Breadboard projects will appear
from time to time with various lessons
in th is course. Kurz Kasch has
suggested that operators and
technicians interested in completing
the breadboard projects could find
the suitable hardware being offered
by AP Products of Euclid, Ohio. AP
Products, which markets through
electronics hobby distributors and
radio and television parts supply
houses, offers an inexpensive bread-
board. Components for the individual
exercises can be gotten from Radio
Shack outlets or from the operator's
own inventory.
Next in the course series, which
continues in PLAY METER, will be
Diode- Transistor Gates (lesson
seven) and Resistor- Transistor Gates
(lesson eight).
Microcomputer
terms reference
For those who are not familiar with
the terms so often used in reference
to microprocessor technology, here
is a brief description of frequently
occurring ones.
RAM is read/write memory which
the microprocessor uses for tempor-
ary storage during the execution of a
program, and to remember which
images are where on the screen in
video games. Unfortunately, as soon
as the power is turned off, this type of
memory device "forgets" all the
information held in it.
Three main types of RAM are
used: dynamic ram, which must be
continually refreshed and is normally
used for memory mapping video
displays; static ram, which is more
expensive but doesn't need to be re-
freshed and is normally used as
"scratch pad;" and CMOS ram,
which is even more expensive but
needs very little current and is
normally used with batteries so that
it doesn't forget information when
the machine is turned off- i.e ., for
storing the electronic bookkeeping
information.
ROM is permanent memory which
is used to store programs and video
game characters. The information is
put in by the semiconductor
manufacturer and cannot be
changed.
PROM is a device which has
information put into it by the manu-
facturer and cannot then be
changed. It is frequently used for
program storage in early production
machines; color information de-
coding in games including Golaxians
and Moon Crestas; storing color
information, as in color Space
lnuaders; and for producing timing
signals and chip selects.
EPROM is a device which can
have information put into it by the
game manufacturers but can be later
"wiped clean" and reprogrammed.
Originally it was only used where
fairly small quantities of a particular
type of machine were to be manu-
factured, but it has become so cheap
recently that it is being used to store
programs and character information
in many current machines. The most
popular EPROMs are the 2708 which
has a capacity of 1K (1,024 bytes)
and the single rail 2716 which
contains 2K (2,048 bytes). Several
types of ROMs used by game
manufacturers can be easily
replaced by 2716 EPROMs.
- from Coin Slot Location
17