Chapter 3
Timing Diagrams
©
National Instruments Corporation
3-7
The NI 653
X
can either drive an output clock signal onto the PCLK line or
receive an input clock signal from the PCLK line. By default, the PCLK
line is set for input during output transfers and for output during input
transfers.
Tip
If you are using long cables, slow the PCLK clock signal to compensate for the
decrease in data setup time.
Figure 3-5.
Burst Input Timing Diagram (Default)
Parameter
Description
Minimum
Maximum
Input Parameters
t
rs
Setup time from REQ valid to PCLK
12
—
t
rh
Hold time from PCLK to REQ invalid
0
—
t
dis
Setup time from input data valid to PCLK
4
—
t
dih
Hold time from PCLK to input data invalid
6
—
Output Parameters
t
pc
PCLK cycle time
50
700
1
t
pw
PCLK high pulse duration
t
pc
/2 – 5
t
pc
/2 + 5
t
pa
PCLK to ACK valid
—
18
t
ah
Hold time from PCLK to ACK invalid
3
—
1
t
pc
= programmable delay from 100 to 700 ns, or 50 ns if programmable delay is 0. Timebase stability for the onboard
20 MHz clock source is 50 ppm.
All timing values are in nanoseconds.
PCLK
ACK
Data In Valid
REQ
t
dis
t
dih
t
rs
t
pa
t
pw
t
pc
t
rh
t
ah