MC74HC595A
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7
FUNCTION TABLE
Operation
Inputs Resulting Function
Reset
Serial
Input
A
Shift
Clock
Latch
Clock
Output
Enable
Shift
Register
Contents
Latch
Register
Contents
Serial
Output
SQ
H
Parallel
Outputs
Q
A
− Q
H
Reset shift register L X X L, H, ↓ L L U L U
Shift data into shift
register
H D ↑ L, H, ↓ L D → SR
A
;
SR
N
→ SR
N+1
U SR
G
→ SR
H
U
Shift register remains
unchanged
H X L, H, ↓ L, H, ↓ L U U U U
Transfer shift register
contents to latch
register
H X L, H, ↓ ↑ L U SR
N
→ LR
N
U SR
N
Latch register remains
unchanged
X X X L, H, ↓ L * U * U
Enable parallel outputs X X X X L * ** * Enabled
Force outputs into high
impedance state
X X X X H * ** * Z
SR = shift register contents D = data (L, H) logic level ↑ = Low−to−High * = depends on Reset and Shift Clock inputs
LR = latch register contents U = remains unchanged ↓ = High−to−Low ** = depends on Latch Clock input
PIN DESCRIPTIONS
INPUTS
A (Pin 14)
Serial Data Input. The data on this pin is shifted into the
8−bit serial shift register.
CONTROL INPUTS
Shift Clock (Pin 11)
Shift Register Clock Input. A low− to−high transition on
this input causes the data at the Serial Input pin to be shifted
into the 8−bit shift register.
Reset (Pin 10)
Active−low, Asynchronous, Shift Register Reset Input. A
low on this pin resets the shift register portion of this device
only. The 8−bit latch is not affected.
Latch Clock (Pin 12)
Storage Latch Clock Input. A low−to−high transition on
this input latches the shift register data.
Output Enable (Pin 13)
Active−low Output Enable. A low on this input allows the
data from the latches to be presented at the outputs. A high
on this input forces the outputs (Q
A
−Q
H
) into the
high−impedance state. The serial output is not affected by
this control unit.
OUTPUTS
Q
A
− Q
H
(Pins 15, 1, 2, 3, 4, 5, 6, 7)
Noninverted, 3−state, latch outputs.
SQ
H
(Pin 9)
Noninverted, Serial Data Output. This is the output of the
eighth stage of the 8−bit shift register. This output does not
have three−state capability.
