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CHAPTER 4
THE
8080 CENTRAL PROCESSOR UNIT
The 8080
is
a complete 8-bit parallel, central processor
unit
(CPU)
for
use
in general purpose digital computer
sys-
tems.
It
is fabricated on a single LSI chip
(see
Figure 1·1).
using Intel's n-channel silicon gate MOS process. The
8080
transfers data and internal state information
via
an
8-bit,
bidirectional
3-state
Data Bus
(00-07).
Memory and peri-
pheral device
addresses
are
transmitted over a separate 16-
Figure
4-1.
8080
Photomicrograph With
Pin
Designations
4-1
bit
3-state Address
Bus
(AO-A 15). Six
timing
and control
outputs
(SYNC, OBIN, WAIT, WR,
HLOA
and
INTE)
eman-
ate
from
the 8080, while
four
control
inputs
(READY,
HOLD,
INT
and
RESET),
four
power inputs (+12v, +5v,
-5v, and GNO) and
two
clock inputs
(4)1
and
4>2)
are
ac-
cepted by the 8080
..
A
IO
40
All
GND
39
38
37
36
35
34
INTEl!
33
8080
32
A6
10
31
As
11
30
12 29
A3
HOLD 13 28
+12V
INT
14 27
A2
15
26
Al
16
25
Ao
17
24
WAIT
WR
18
23
READY
SYNC
19 22
01
+5V
20
21
HLDA