National Instruments 653X - Manual (Page 25)

Chapter 2 Using Your 653X
© National Instruments Corporation 2-7 653X User Manual
Deciding Which Handshaking Protocol to Use
The 653X device supports several different handshaking protocols to
communicate with your peripheral device. The protocol you select will
determine the timing of the ACK and REQ signals.
From the perspective of the 653X device, the peripheral device requests
the transfer of data by signaling on the REQ line. The 653X device
acknowledges it is ready to transfer data by signaling on the ACK line.
Use Table 3-1, Handshaking Protocol Characteristics , to select a
handshaking protocol for your application. To select a protocol compatible
with your peripheral device, compare the handshaking sequence and state
machine diagrams for each protocol in the later sections of Chapter 3,
Timing Diagrams .
Using the Burst Protocol
The burst protocol differs from all the other handshaking protocols in that
it is the only synchronous (clocked) protocol. In addition to ACK and REQ,
the 653X and peripheral device share a clock signal over the PCLK line.
See Chapter 3,
Timing Diagrams , for more information about the burst
protocol.
If you want to acquire or generate patterns of every edge of a clock
signal, see the
Generating and Receiving Digital Patterns and
Waveforms—Pattern I/O section.
Note Feed external clocking signals into the PCLK pin for burst-mode handshaking and
into the REQ pin when performing pattern I/O.
Deciding the PCLK Signal Direction
The 653X device can receive an external PCLK signal to control data
transfers or generate a PCLK signal using an internal 32-bit counter to
output to the peripheral device. By default, the 653X device generates the
PCLK signal for input operations and receives an external PCLK signal for
output operations.