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+V DD
A in
1
"FORM A"
CONTACT
7
OSC in
OSCILLATOR
AND
C ext
9
TWO–PHASE
CLOCK GENERATOR
OSC out
The single most important characteristic of the MC14490
is that it works with a single signal lead as an input, making
it directly compatible with mechanical contacts (Form A
and B).
The circuit has a built–in pullup resistor on each input. The
worst case value of the pullup resistor (determined from the
Electrical Characteristics table) is used to calculate the con-
tact wetting current. If more contact current is required, an
external resistor may be connected between V DD and the
input.
Because of the built–in pullup resistors, the inputs cannot
be driven with a single standard CMOS gate when V DD is be-
low 5 V. At this voltage, the input should be driven with paral-
FROM CONTACTS
MC14490
6–214
PULLUP RESISTOR
(INTERNAL)
4–BIT STATIC SHIFT REGISTER
SHIFT
φ 1
φ 2
Figure 4. Typical "Form A" Contact Debounce Circuit
(Only One Debouncer Shown)
OPERATING CHARACTERISTICS
1/6 MC14050
C ext
OSC in
7
9
OSC out
TO SYSTEM
MC14490
LOGIC
Figure 5. Typical Single Oscillator Debounce System
DATA
1/2 BIT
DELAY
LOAD
φ 1 φ 2
φ 1 φ 2
leled standard gates or by the MC14049 or MC14050
buffers.
The clock input circuit (pin 7) has Schmitt trigger shaping
such that proper clocking will occur even with very slow clock
edges, eliminating any need for clock preshaping. In addi-
tion, other MC14490 oscillator inputs can be driven from a
single oscillator output buffered by an MC14050 (see Fig-
ure 5). Up to six MC14490s may be driven by a single buffer.
The MC14490 is TTL compatible on both the inputs and
the outputs. When V DD is at 4.5 V, the buffered outputs can
sink 1.6 mA at 0.4 V. The inputs can be driven with TTL as a
result of the internal input pullup resistors.
OSC in 7
FROM
MC14490
CONTACTS
OSC in 7
FROM CONTACTS
MC14490
MOTOROLA CMOS LOGIC DATA
15
A out
NO CONNECTION
9 OSC out
TO SYSTEM
LOGIC
NO CONNECTION
9 OSC out
TO SYSTEM
LOGIC
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