HD74AC HITACHI [Hitachi Semiconductor], HD74AC Datasheet - Page 27

• Manufacturer Part Number: HD74AC
• Description: HD74AC Series Common Information
• Manufacturer: HITACHI [Hitachi Semiconductor]

Definition of Specifications
Vmi = 50% V
Vmo = 50% V
3.5 Enable and Disable Times
Figures 5 and 6 show that the disable times are measured at the point where the output voltage has risen or
fallen by 10% from the voltage rail level (i.e., ground for t
repeatability of measurements, reduces test time, and gives the system designer more realistic delay times
to use in calculating minimum cycle times. Since the high-impedance state rising or falling waveform is
RC-controlled, the first 10% of change is more linear and is less susceptible to external influences. More
importantly, perhaps from the system designer’s point of view, a change in voltage of 10% is adequate to
ensure that a device output has turned off. Measuring to a larger change in voltage merely exaggerates the
apparent Disable time and thus penalizes system performance since the designer must use the Enable and
Disable times to device worst case timing signals to ensure that the output of one device is disabled befor
that of another device is enabled.
Vmi = 50% V
Vmo = 50% V
26
CC
CC
CC
CC
for HD74AC devices; 1.5 V for HD74ACT devices
for HD74AC devices; 1.5 V for HD74ACT devices
for HD74AC/HD74ACT devices
for HD74AC/HD74ACT devices
Figure 4 Propagation Delay, Pulse Width, and t
Figure 5 3-State Output High Enable and Disable Times
OUTPUT
CONTROL
DATA
OUT
CONTROL
IN
CLOCK
OUTPUT
t
ZH
Vmo
t
PHL
Vm
tw
LZ
–0.3 V
t
HZ
or V
CC
Vmi
for t
t
rec
Vmi
HZ
rec
t
Vmo
Vmi
PLH
) . This change enhances the
V
90% V
Waveforms
CC
CC