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Chapter 3 Timing Diagrams
653X User Manual 3-4 ni.com
Handshaking I/O Timing Diagrams
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
Comparing the Different Handshaking Protocols
For an overview of all handshaking protocols supported by your
653X device, see Table 3-1.
Note
Whether an ACK or a REQ signal occurs first in the handshaking sequence depends
on the protocol and the direction of the transfer.
Table 3-1.
Handshaking Protocol Characteristics
Protocol
REQ/ACK
Polarity
Which REQ Edge
Requests Transfer
Where the
Programmable
Delay Is Located
Complementary Protocol(s)
Asynchronous Protocols
8255
Emulation
Active-low Trailing Between transfers Long Pulse
Level ACK Programmable Leading Before ACK
and between transfers
Level ACK
Leading-Edge Programmable Leading Before ACK
and between transfers
Leading Edge
Long Pulse Programmable Leading Pulse width and
between transfers
Long Pulse, 8255 Emulation,
and 8255
Trailing-Edge Programmable Trailing Pulse width and
between transfers
Trailing-Edge