National Instruments 653X Manuale Utente

© National Instruments Corporation

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.

Burst

Programmable

Neither (level REQ)

Clock speed

Burst

 * 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

Table 3-1.  Handshaking Protocol Characteristics (Continued)