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Data Transfer Modes
The HP E1432A can be programmed to use either of two data transfer
modes: overlap block mode and continuous mode. To help explain these
modes we will first describe block mode.
Block Mode (HP E1431A)
The HP E1432A’s overlap block mode is similar the block mode which is
used in other Hewlett-Packard instruments such as the 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 HP E1432A’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 HP E1432A’s and the 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 HP E1432A’s overlap block mode can be configured to act similarly to
continuous mode, but not identically. The HP E1432A 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.
HP E1432A User's Guide
The C-Language Host Interface Library
4-24