Chapter 5 Signal Timing
© National Instruments Corporation 5-19 DIO 6533 User Manual
Long-Pulse Mode
Long-pulse mode is a variant of leading-edge mode. The only
difference is the effect of a data-settling delay, if used. In long-pulse
mode, a programmable delay, rather than delaying the ACK pulse,
increases the minimum width of the pulse.
Long-pulse mode enables you to handshake with a peripheral device
that requires a large minimum pulse width.
Long-pulse mode also enables you to handshake with 8255 emulation
mode, if you set the ACK and REQ signals to active low. If you want to
use long-pulse mode to handshake with an actual 8255 or 82C55 PPI,
make sure you select an adequate minimum pulse width for your 8255
or 82C55. A data-settling delay of 500ns is sufficient for any current
8255 or 82C55 PPI. Figures5-16 and 5-17 show long-pulse mode input
and output diagrams, respectively.
Figure 5-16. Long-Pulse Mode Input
Wait
For
Space
Wait
For
REQ
Programmable
Delay
Programmable
Delay
Wait
For
REQ
When REQ
Asserted
When 6533 Device
Has Space For Data,
Input Data*
Clear
ACK
Pulse
When REQ
Unasserted
Initial State
ACK Cleared
Send
ACK Pulse
* With REQ-edge latching enabled, the data read
is from the last active-going REQ edge.