Handshaking I/O Timing Diagrams; Comparing The Different Handshaking Protocols - National Instruments 653X User Manual

Chapter 3 Timing Diagrams

Handshaking I/O Timing Diagrams

Comparing the Different Handshaking Protocols

Note Whether an ACK or a REQ signal occurs first in the handshaking sequence depends
on the protocol and the direction of the transfer.
REQ/ACK
Protocol Polarity
Asynchronous Protocols
8255 Active-low
Emulation
Level ACK Programmable
Leading-Edge Programmable
Long Pulse Programmable
Trailing-Edge Programmable
653X User Manual
This section compares of the handshaking I/O protocols and includes
timing diagrams for each:
• Handshaking sequence for input operation
• State machine for input operation
• Timing specification for input operation
• Handshaking sequence for output operation
• State machine for output operation
• Timing specification for output operation
For an overview of all handshaking protocols supported by your
653X device, see Table 3-1.
Table 3-1. Handshaking Protocol Characteristics
Which REQ Edge
Requests Transfer
Trailing
Leading
Leading
Leading
Trailing
Where the
Programmable
Delay Is Located
Between transfers
Before ACK
and between transfers
Before ACK
and between transfers
Pulse width and
between transfers
Pulse width and
between transfers
3-4
Complementary Protocol(s)
Long Pulse
Level ACK
Leading Edge
Long Pulse, 8255 Emulation,
and 8255
Trailing-Edge
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