VXI VT1433B - Manual (Page 70)

Data Transfer Modes
The VT1433B can be programmed to use either of two data transfer modes:
overlap block mode and continuous mode. Block mode will be discussed first.
Block Mode (Agilent/HP E1431A)
The VT1433B’s overlap block mode is similar the block mode which is used in
some Agilent instruments such as the Agilent/HP E1431A. In block mode, the
input hardware acquires one block after getting an arm and trigger. It does not
allow the system to trigger until it is ready to process the trigger and it acquires
pre-trigger data if necessary. The hardware does not accept a new arm and trigger
until the acquired block is sent to the host. There is no provision for overlap or
queuing up more than one block when in block mode. There is also no way for
a FIFO overflow to occur.
The VT1433B’s overlap block mode can be configured to act exactly like
traditional block mode. It also has additional capabilities as described below.
Continuous Mode
Both the VT1433B and the Agilent/HP E1431A use continuous mode. In this
mode, the input hardware waits for an arm and trigger and then starts acquiring
data continuously. If the host is slow, several blocks can be queued up in the
input hardware. If the host gets far enough behind, a FIFO overflow occurs and
the input stops acquiring data.
The VT1433B’s overlap block mode can be configured to act similarly to
continuous mode, but not identically. The VT1433B can also use the traditional
continuous mode.
Overlap Block Mode
Overlap block mode combines features of both block mode and continuous mode.
The main difference between overlap block mode and traditional block mode is
that overlap block mode allows additional arms and triggers to occur before an
already-acquired block is sent to the host. A trigger can occur before the end of
the previous block, so overlapping blocks are possible (hence the name “overlap
block mode”). As in continuous mode, there is an overlap parameter which
controls how much overlap is allowed between consecutive blocks.
VT1433B User's Guide
Using the VT1433B
3-32