ADSP-218xN Series
TIMING SPECIFICATIONS
This section contains timing information for the DSP’s
external signals.
General Notes
Use the exact timing information given. Do not attempt to
derive parameters from the addition or subtraction of
others. While addition or subtraction would yield meaning-
ful results for an individual device, the values given in this
data sheet reflect statistical variations and worst cases. Con-
sequently, parameters cannot be added up meaningfully to
derive longer times.
Timing Notes
Switching characteristics specify how the processor changes
its signals. Designers have no control over this timing—
circuitry external to the processor must be designed for
compatibility with these signal characteristics. Switching
characteristics tell what the processor will do in a given
circumstance. Switching characteristics can also be used to
ensure that any timing requirement of a device connected
to the processor (such as memory) is satisfied.
Timing requirements apply to signals that are controlled by
circuitry external to the processor, such as the data input
for a read operation. Timing requirements guarantee that
the processor operates correctly with other devices.
Frequency Dependency For Timing Specifications
tCK is defined as 0.5 tCKI. The ADSP-218xN uses an input
clock with a frequency equal to half the instruction rate. For
example, a 40 MHz input clock (which is equivalent to
25 ns) yields a 12.5 ns processor cycle (equivalent to
80 MHz). tCK values within the range of 0.5 tCKI period
should be substituted for all relevant timing parameters to
obtain the specification value.
Example: tCKH = 0.5 tCK – 2 ns = 0.5 (12.5 ns) – 2 ns= 4.25 ns
Output Drive Currents
Figure 19 shows typical I-V characteristics for the output
drivers on the ADSP-218xN series.The curves represent the
current drive capability of the output drivers as a function
of output voltage.
Figure 21 shows the typical power-down supply current.
Capacitive Loading
Figure 22 and Figure 23 on page 26 show the capacitive
loading characteristics of the ADSP-218xN.
80
60
VOH
VDDEXT = 3.6V @ –40؇C
VDDEXT = 3.3V @ +25؇C
40
VDDEXT = 2.5V @ +85؇C
20
0 VDDEXT = 1.8V @ +85؇C
–20
VDDEXT = 3.6V @ –40؇C
–40
VOL
VVDDDDEEXXTT==11.8.8/2/2.5.5VV@@++8855؇C؇C
VDDEXT = 3.3V @ +25؇C
–60
–80
0
0.5
1.0 1.5
2.0 2.5
3.0 3.5 4.0
SOURCE VOLTAGE – V
Figure 19. Typical Output Driver Characteristics
for VDDEXT at 3.6 V, 3.3 V, 2.5 V, and 1.8 V
REV. 0
–25–