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18243
GUARANTEED
WORST
CASE
CURRENT
SINKING
CAPABiliTIES
OF
ANY
1/0
PORT
PIN
vs.
TOTAL
SINK
CURRENT
OF
All
PINS
3 4 5
6
7 8
9
10
11
12 13
MAXIMUM SINK CURRENT ON ANY PIN@.45V
MAXIMUM
IOL
WORST CASE PIN
(rnA)
Sink Capability
The 8243 can sink 5 mA@.45V
on
each of
its
16110
lines
simultaneously.
If, however, all lines are not sinking
simultaneously
or
all lines are not fully loaded, the drive
capability
of
any individual line increases
as
is shown by
the accompanying curve:
For
example,
if
only 5
of
the
16
lines are
to
sink current
at one time, the curve shows that each
of
those 51ines is
capable
of
sinking 9 mA@.45V (if any lines are
to
sink
9 mA the
total IOl must not exceed
45
mA
or
five 9
mA
loads).
Example:
How many pins can drive 5 TTL loads
(1.6
mAl
assuming remaining pins are unloaded?
IOl
= 5 x
1.6
mA = 8 mA
dOL = 60 mA from curve
#
pins=
60
mA-+-
8 mA/pin =
7.5=
7
In
this
case, 7 lines can sink 8 mA for a total
of
56
mAo
This leaves 4 mA sink current capa·
bility
which can
be
divided in any way among
the remaining 8
110
lines
of
the
8243.
Example: This example shows how the use
of
the
20
mA
sink capability of Port 7
affects
the sink-
ing capability of the
other
110
lines.
An
8243 will drive the
following
loads simul-
taneously.
2 loads -
20
mA@1V (port 7 only)
8 loads - 4 mA@.45V
6
loads -
3.2
mA@.45V
Is
this
within the specified limits?
d
Ol
=(
2 x
20)+(8
x
4)+(6
x 3.2)=91.2
mAo
From the curve:
for
IOl = 4 mA, dOL:::
93
mA
since
91.2
mA <
93
mA the loads are within
specified
limits.
Although
the
20
mA@
1V
loads are used in
calculating
dOL,
it is the largest current
re-
quired@.45V which determines the maximum
allowable
dOL.
Note: A
10
to
50Kn
pullup resistor to +5V should
be
added
to 8243 outputs
when
driving to 5V CMOS directly.
6-67
AFN-00s81A-05