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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 reception
of
data. The selection of
the port comes from the device selection
logic.(OS1·
OS2)
VII. 808GA Status Latch
Here the 8212 is used
as
the status latch
for
an
8080A
microcomputer system. Tha input to the 8212 ;atch
Is
directly from the 8080A data bus. Timing shows that when
the
SYNC signal is true, which is connected 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.
/:
0
1
O
2
0
3
0
4
8080A 0
5
0
6
0
7
SYNC
DB IN
\11
\12
22
15
12V"
ovJ
'-
."""
l----,
CLOCK GEN.
Io
DRIVER
10
9
8
7
3
4
5
6
19
r!1-
--4
~
7
9
16
18
20
~Tl)
22
r;1
0
1
OUTPUT PORT (WITH HAND-SHAKING)
DATA
SYSTEM
INTERRUPT
BUS
r----
....
- OUTPUT STROBE
STB
SYSTEM
OUTPUT
SYSTEM
RESET
}
PORT
SELECTION
L--'-'
____
-
:~~~2~ONTROL)
Note: The mode signal
Is
tied high so thatthe output on the
iatch is active and enabied aii the time.
It is shown that the two areas of concern are the bl-
di rectional data bus
ofthe
microprocessor and the control
bus.
DATA
BUS
STATUS
LATCH
Do
4-
~
rfu-
r,s
8212 P,t-
ffg-
rt""
r:-
INTA
wo
11 T2
STACK
HLTA
~1
OUr
BASIC
Ml
CONTROL
¢2
INP
BUS
MEMR
SYNC
CLR
DS
2
MD
OS1
13
12
'('1
DATA
DBIN
STATUS
8-28
AFN..(J0731Ao05