ADSP-21xx
–24–
REV. B
SPECIFICATIONS (ADSP-2111)
The decay time, tDECAY, is dependent on the capacitative load,
CL, and the current load, iL, on the output pin. It can be
approximated by the following equation:
t
DECAY =
C
L × 0.5 V
i
L
from which
tDIS = tMEASURED – tDECAY
is calculated. If multiple pins (such as the data bus) are dis-
abled, the measurement value is that of the last pin to stop
driving.
Output Enable Time
Output pins are considered to be enabled when they have made
a transition from a high-impedance state to when they start
driving. The output enable time (t ENA) is the interval from
when a reference signal reaches a high or low voltage level to
when the output has reached a specified high or low trip point,
as shown in Figure 21. If multiple pins (such as the data bus)
are enabled, the measurement value is that of the first pin to
start driving.
TEST CONDITIONS
Figure 20 shows voltage reference levels for ac measurements.
Figure 20. Voltage Reference Levels for AC Measurements
(Except Output Enable/Disable)
Output Disable Time
Output pins are considered to be disabled when they have
stopped driving and started a transition from the measured
output high or low voltage to a high impedance state. The
output disable time (tDIS) is the difference of tMEASURED and
tDECAY, as shown in Figure 21. The time tMEASURED is the
interval from when a reference signal reaches a high or low
voltage level to when the output voltages have changed by 0.5 V
from the measured output high or low voltage.
3.0V
1.5V
0.0V
2.0V
1.5V
0.8V
INPUT
OUTPUT
Figure 22. Equivalent Device Loading for AC Measurements
(Except Output Enable/Disable)
2.0V
1.0V
t
ENA
REFERENCE
SIGNAL
OUTPUT
t
DECAY
VOH (MEASURED)
OUTPUT STOPS
DRIVING
OUTPUT STARTS
DRIVING
t
DIS
t
MEASURED
VOL (MEASURED)
VOH (MEASURED) – 0.5V
VOL (MEASURED) +0.5V
HIGH-IMPEDANCE STATE.
TEST CONDITIONS CAUSE
THIS VOLTAGE LEVEL TO BE
APPROXIMATELY 1.5V.
VOH (MEASURED)
VOL (MEASURED)
Figure 21. Output Enable/Disable
TO
OUTPUT
PIN
50pF
+1.5V
IOH
IOL