National Instruments DIO 6533 - Manual (Page 64)

Chapter 5 Signal Timing
© National Instruments Corporation 5-5 DIO 6533 User Manual
6533 device emulation mode is a superset of the 8255 and 82C55
protocols. The PCI-DIO-32HS can handshake with peripheral devices
that use 8255 or 82C55 handshaking specifications.
The 6533 device can perform back-to-back transfers much faster than a
true 8255-based device. If your peripheral device requires more time
between transfers, you can configure the 6533 device to add a
data-settling delay between transfers.
You can use a 6533 device in emulation mode with 8, 16, or 32-bit data
paths.
Input
Note: 6533 device terminology differs from 8255 terminology. In input mode,
the 6533 device REQ line carries the 8255 STB input signal, and the
6533 device ACK line carries the 8255 IBF output signal. Both lines are
active low.