Chapter3 TimingDiagrams
653XUser Manual 3-2 ni.com
Figure3-1. InternalRequest Timing Diagram
External REQ Signal Source
Use anexternal request when you wa ntto time datatransfers using an
external signal on the REQ pin of the I/O connector. You can select the
polarity of the REQ signal. If active high (default), the 653Xdevice will
latchthe data on the I/O pins on therisingedge of the REQ signal. If active
low,the 653Xdevice will latch the data on the I/O pins on the falling edge
ofthe REQ signal. The low time and high time of the REQ signal must each
be >20 ns.The minimumduration for a period of the REQ signal is 50 ns.
Note Fordata transfers that use a hardware start trigger, there is no mandatory setup (tsu)
or hold time (th) for the STARTRIG(ACK) signal. It can be asserted at any point before,
Parameter Description
tc*Cycle time
tw*Width of pul se
tpPropagation time to validoutput data
tsu Setup time
thHold time
*The 6534 devices will transfer data at 20 MHz when the cycle time (tc) for REQ pulse is 50 ns and width of the REQ
pulse(tw) is 20–30 ns.
dtpwill remove bar
DataValid
(OutputMode)
DataValid
(InputMode) tsu
30ns
Min
th
0ns
Min
tp
30ns
Max
tc
Programmable= Interval x Timebase
Programmable= One Timebase
REQif Active High
REQif Active Low
tw