National Instruments NI-VXI User Manual
Page 90
Chapter 3 Software Overview
NI-VXI User Manual
3-52
© National Instruments Corporation
maximum time from source assertion edge). The accepting
device(s) can later unassert the trigger line (no maximum time is
specified) to complete the handshake.
•
START/STOP—START/STOP is a one-line, multiple-device
protocol. START/STOP can be sourced only by the VXI Slot 0
device and sensed by any other devices on the VXI backplane. The
START/STOP protocol is synchronized with the backplane clock
(CLK10 for TTL, CLK100 and SYNC100 for ECL) onto any one
of the trigger lines. A START condition is generated on the
assertion edge on the trigger line, and a STOP condition is
generated on the unassertion edge of the trigger line.
•
ON/OFF—ON/OFF protocol is identical to the START/STOP
protocol. The VXIbus specification, however, defines
START/STOP such that only Slot 0 may assert START/STOP.
Therefore, ON/OFF protocols are outside the VXIbus specifications
but provide similar functionality.
You can use these protocols in any way that your application requires.
You can use them for device synchronization, for stepping through
tests, or for a command path. The NI-VXI trigger functions have been
designed to accommodate all trigger lines and the protocols for all
appropriate TTL and ECL VXI trigger lines (SYNC, ASYNC,
SEMI-SYNC, START/STOP, and ON/OFF).
The VXI trigger functions have been grouped into the following four
categories:
•
Source trigger functions
•
Acceptor trigger functions
•
Map trigger functions
•
Trigger configuration functions
The actual capabilities of specific systems are based on the triggering
capabilities of the hardware devices involved (both the sourcing and
accepting devices). All of the NI-VXI functions have appropriate error
response for unsupported capabilities.
Capabilities of the National Instruments Triggering Hardware
The NI-VXI trigger functions are a general-purpose interface designed
to accommodate most uses of VXI triggers. The actual capabilities of a
particular platform will always be a subset of these capabilities. In