Using The Burst Protocol - National Instruments 653X User Manual

REQ/ACK
Protocol Polarity
Synchronous Protocol
Burst Programmable
* Asynchronous protocols can compensate automatically to cable length, yet for synchronous protocols, you need to select
an appropriate speed for your cable when configuring your device.
Select a delay of at least the following:
• 0 for a typical cable up to 1 m
• 1 (70 ns) for a typical cable up to 5 m
• 2 (140 ns) for a typical cable up to 15 m long

Using the Burst Protocol

© National Instruments Corporation
Table 3-1. Handshaking Protocol Characteristics (Continued)
Which REQ Edge
Requests Transfer
Neither (level REQ)
In order for the 653X device to communicate with peripheral devices in
handshaking mode, it is important to verify that:
• You are using complementary protocols. For example, use
8255-emulation protocol with long-pulse protocol.
• The ACK/REQ polarity are the same. For example, 8255 emulation
is active low only, so the other device must use the long-pulse protocol
and have active low ACK/REQ polarity.
Burst protocol is a synchronous, or clocked, protocol. In addition to using
the ACK and REQ signals like the other handshaking protocols, in burst
protocol, the 653X device and the peripheral device share a clock signal
over the PCLK line.
The 653X device asserts the ACK signal if it is ready to perform a transfer.
If the peripheral device also asserts the REQ signal indicating it is ready,
a transfer occurs on the rising edge of the PCLK signal. See Figures 3-3
and 3-4 for examples of burst protocol transfers. Dashed lines indicate
when data is transferred.
Where the
Programmable
Delay Is Located
Clock speed
3-5
Chapter 3 Timing Diagrams
Complementary Protocol(s)
Burst
653X User Manual