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SCHOTTKY BIPOLAR
8212
VI. Output Port (With Hand-Shaking)
The
8212
can be used to transmit data from the data
bus to a system output. The output strobe could be
a hand-shaking signal such
as
"reception
of
data"
from the device that the system is outputting to. It
in turn, can interrupt the system signifying the re-
ception
of
data. The selection
of
the port comes
from the device selection logic. (OS1·
OS2)
SYSTEM
INTERRUPT
OUTPUT PORT (WITH HAND-SHAKING)
DATA
BUS
r----~-
OUTPUT STROBE
STB
8212 SYSTEM OUTPUT
INT
CLR
11.>----...--
SYSTEM RESET
}
PORT SELECTION
(LATCH
CONTROL)
L..--
..._-
(OS1.0S2)
VII.
8080
Status Latch
Here the 8212 is used as the status latch for
an
8080
microcomputer system. The input to the 8212 latch
is directly from the 8080 data bus. Timing shows
that when the SYNC signal is true, which is con-
nected to the
OS2
input and the phase 1 signal is
true, which is a TTL level coming from the
clock
generator; then, the status data will be latched into
the 8212.
Note: The mode signal is tied high so that the output
on
the latch is active and enabled all the time.
It is shown that the
two
areas
of
concern are the
bidirectional data bus
of
the microprocessor and the
control bus.
8080 STATUS LATCH
OATA
BUS
INTA
WO
T1
T2
STACK
HLTA
</>1
OUT
M1
BASIC
</>2
INP
CONTROL
MEMR
BUS
SYNC
OATA
OBIN
STATUS
DO
10
9
0,
8
°2
7
°3
3
8080
°4
4
Os
5
°6
6
°7
SYNC
19
OBIN
17
-
</>1
</>2
STATUS
22
15
LATCH
3
0,
°0
4
"'"'---
I---
5
6
~)
7
I---
-4
L-
9
~
16
J..L
18
8212
17
20
~
19
--
22
~
21
CLOCK GEN.
(</>1TTL)
I---
&
DRIVER
I""--
r<:
CLR
14
OS2
MO OS,
·13
12
11
I I
I
12V
f\
ovJ
\..
5-105