adsp-21msp58 Analog Devices, Inc., adsp-21msp58 Datasheet - Page 37

• Manufacturer Part Number: adsp-21msp58
• Description: Dsp Microcomputers
• Manufacturer: Analog Devices, Inc.

REV. 0
Output Disable Time
Output pins are considered to be disabled when they have
stopped driving and started a transition from the measured out-
put high or low voltage to a high impedance state. The output
disable time (t
shown in the Output Enable/Disable diagram. The time is the
interval from when a reference signal reaches a high or low volt-
age level to when the output voltages have changed by 0.5 V
from the measured output high or low voltage. The decay time,
t
rent load, i
following equation:
from which
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.
DECAY
, is dependent on the capacitative load, C
L
, on the output pin. It can be approximated by the
DIS
) is the difference of t
t
DIS
t
DECAY
t
MEASURED
C
L
• 0.5V
i
L
– t
MEASURED
DECAY
L
and t
, and the cur-
DECAY
, as
–37–
Output Enable Time
Output pins are considered to be enabled when that have made
a transition from a high-impedance state to when they start driv-
ing. The output enable time (t
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 the Output Enable/Disable diagram. If multiple pins (such as
the data bus) are enabled, the measurement value is that of the
first pin to start driving.
V
V
OH
OL
(MEASURED)
REFERENCE
(MEASURED)
SIGNAL
OUTPUT
Figure 31. Output Enable/Disable
OUTPUT STOPS
t
t
M EASURED
DIS
DRIVING
HIGH-IMPEDANCE STATE. TEST CONDITIONS CAUSE
THIS VOLTAGE LEVEL TO BE APPROXIMATELY 1.5V.
V
V
t
OH
OL
DECAY
(MEASURED) +0.5V
ADSP-21msp58/59
(MEASURED) –0.5V
ENA
) is the interval from when a
OUTPUT STARTS
2.0V
1.0V
t
ENA
HERE
V
(MEASURED)
V
(MEASURED)
OH
OL