External Req Signal Source - National Instruments 653 Series User Manual

Chapter 3 Timing Diagrams
dtp will remove bar
REQ
if Active Low
REQ
if Active High
Data Valid
(Output Mode)
Data Valid
(Input Mode)
Parameter
t
*
c
t
*
w
t
p
t
su
t
h
* The NI 6534 transfers data at 20 MHz when the cycle time (t
is 20–30 ns.

External REQ Signal Source

NI 653X User Manual
Programmable:
t = Interval x Timebase Period
c
t
c
t = One Timebase Period
w
t
su
30 ns
Min
Cycle time
Width of pulse
Propagation time to valid output data
Setup time
Hold time
Figure 3-1. Internal Request Timing Diagram
Use an external request when you want to time data transfers using an
external signal on the REQ pin of the I/O connector. You can select the
polarity of the REQ signal. If you choose active high (default), the NI 653X
latches the data on the I/O pins on the rising edge of the REQ signal. If you
choose active low, the NI 653X latches the data on the I/O pins on the falling
edge of the REQ signal. The low time and high time of the REQ signal must
each be >20 ns. The minimum duration for a period of the REQ signal is
50 ns.
Programmable:
t
w
t
p
30 ns
Max
t
h
0 ns
Min
Description
) for REQ pulse is 50 ns and width of the REQ pulse (t
c
3-2
)
w
ni.com