National Instruments DIO 6533 - Manual (Page 41)

Chapter 3 Hardware Overview
DIO 6533 User Manual 3-12 © National Instruments Corporation
Starting a Handshaking Transfer
Starting a handshaking transfer correctly protects against incorrect or
missed data when the ACK and REQ lines are changing polarity to
active-high or active-low. This is particularly important in burst mode
because of the potential to miss a lot of data. You can use either of the
following two startup methods:
• Control the configuration and startup sequence.
• Select compatible line polarities and default line levels.
Controlling the Startup Sequence
One startup method is to follow a prescribed initialization order in
which you can make sure the 6533 device is configured and is driving
a valid ACK value before you enable the transfer on the peripheral
device. Similarly, you can make sure the peripheral device is configured
and is driving a valid REQ value before you enable the transfer on the
6533 device.
To use a prescribed initialization order, perform the following steps:
1. Configure the 6533 device for a protocol compatible with your
peripheral device.
2. Configure and reset the peripheral device, if appropriate.
3. Enable the input device (6533 device or peripheral device) and
begin a transfer.
4. Enable the output device (6533 device or peripheral device) and
begin a transfer.
To control the startup order, you must be able to enable and disable the
peripheral device, and you must control the order in which the 6533
device and the peripheral device are enabled. The 6533 device extra
input and output lines can be helpful for these purposes.
Controlling the startup sequence does not apply to buffered (block)
operations. In a buffered operation, the NI-DAQ software configures
and enables the 6533 device at the same time, when you start the actual
data transfer. For buffered operations, therefore, use the second startup
method, controlling the line polarities.