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8212
Applications of the
8212
.....
For
Microcomputer Systems
I Basic Schematic Symbol
II
Gated Buffer
III BI-Directlonal
Bus Driver
IV
Interrupting Input Port
1.
Basic Schematic Symbols
Two
examples
of
ways
to
draw the 8212 on system
schematics -
(1)
the top being, the detailed view showing
pin numbers, and (2) the bottom being the symbolicview
BASIC SCHEMATIC SYMBOLS
INPUT DEVICE
11
STB
4
01
DO
6
8
9
10
V Interrupt Instruction
Port
VI
Output Port '
VII '8080A,$,tatus Latch
VIII
8085A'-Address Latch
showing the system input or output
as
a system bus (bus
containing 8
parallel lines). The output
to
the data bus is
symbolic
In
referencing 8 parallel lines.
OUTPUT DEVICE
11
~
01
STB
DO
:
16
8212
15
18
(DETAILED)
GND
INPUT
STROBE----;:=L...,
17
19
Vee
..
_..c:::;~--
OUTPUT,
FLAG
SYSTEM
INPUT
(SYMBOLIC)
SYSTEM
OUTPUT
GND
DATA
BUS
II. Gated Butter (3-State)
The simplest use of the
82121s that of a gated butter. By
tying the mode signal low and the strobe input high, the
data latch is acting
as
a straight through gate. The output
buffers are then enabled from the device selection logic
DS1
and
DS2.
'
When the device selection logic is false, the outputs are 3-
state.
'
When the device selection logic is true, the input data from
the system is directly transferred
to
the output. The input
data load Is
250
micro amps. The output data can sink
15
milll amps. The minimum high output is
,3.65
volts.
GATED BUFFER
vcc--~-----.---~
8-26
INPUT
DATA,
(250.AI
STB
8212
~----<ilCLIf
GATING {
CONTROL
(m.DS2)
,
__
-:-_----,-_---.J
OUTPUT
DATA
(15mA)
(3.65V
MIN)
AFN.(JQ731
A-OG