Selecting Ack/Req Signal Polarity; Choosing Whether To Use A Programmable Delay - National Instruments NI 653 Series User Manual

Selecting ACK/REQ Signal Polarity

Choosing Whether to Use a Programmable Delay

© National Instruments Corporation
For all handshaking protocols except 8255 emulation, you can set the
polarity of the ACK and REQ signals to active high or active low through
software. By default, these signals are active high in NI-DAQ functions and
active low in LabVIEW VIs. Refer to Table C-1,
68-Pin Assignments, for an overview of all control/timing trigger lines.
For all the protocols, you can set a programmable delay. A programmable
delay is useful when the handshaking signals of the NI 653X occur faster
than the peripheral device can handle.
For all protocols except burst, the delay increases the time before the
NI 653X can respond to the REQ signal. For the burst protocol, the
programmable delay selects the frequency of the clock signal when you use
an internally generated clock source. You can change the PCLK frequency
by modifying the ACK Modify Amount parameter of the Digital Mode
Config VI or the ACK Delay Time attribute of the
in NI-DAQ C interface. Use the following table to find the resulting period
in nanoseconds. The PCLK frequency is then selected by NI-DAQ based on
this choice.
PCLK Period in ns
50
100
200
300
400
500
600
700
The state machine diagrams in Chapter 3,
precisely where this delay occurs in the handshaking sequence.
PCLK Frequency in MHz
Timing
2-19
Chapter 2 Using Your NI 653X
NI 653X I/O Connector
function
DIG_Grp_Mode
20
10
5
3.33
2.5
2
1.66
1.43
Diagrams, show more
NI 653X User Manual