Interrupter - National Instruments Corporation GPIB-1014P User Manual

General Description

Interrupter

Interrupt events that originate from the TLC are as follows:
• GPIB Data In (DI)
• GPIB Data Out (DO)
• END message received (END RX)
• GPIB Command Out (CO)
• Remote mode change (REMC)
• GPIB handshake error (ERR)
• Lockout change (LOKC)
• Address Status Change (ADSC)
• Secondary Address received (APT)
• Service Request received (SRQI)
• Trigger command received (DET)
• Device Clear received (DEC RX)
• Unrecognized Command received (CPT)
All 13 interrupt events are wire-ORed in the TLC to a single signal designated INT on the interface
board. When one of these events occurs, INT goes high and one of the interrupt request lines
(IRQ1* through IRQ7*) is driven low. You select the interrupt request line by means of an
onboard jumper. You set the interrupt priority via three hardware switches (U28). The encoded
value of the priority must match the level of the interrupt request line. See Interrupt Request Line
Selection in Section Three for more information on setting the interrupt level.
The onboard hardware implements the VMEbus interrupt acknowledge protocol. The interrupter
drives the VMEbus with an 8-bit Status/ID byte (vector) during an interrupt acknowledge cycle.
This Status/ID byte is set by an onboard 8-position Dual In-line Package (DIP) switch (U7). After
the interrupt handler reads the Status/ID byte from the data bus, it releases the data strobe DS0* to
high. Upon seeing DS0* high, the interrupter releases the data bus and the interrupt request line.
This implies that the GPIB-1014P interrupter is a Release On Acknowledge (ROAK) interrupter.
Note: Even though the interrupt request line is no longer driven, the TLC Interrupt (INT) line
remains asserted until it is cleared in the interrupt service routine by reading the appropriate
status register (ISR1 or ISR2). Clearing the TLC INT line in the interrupt routine enables
further interrupts from the GPIB-1014P.
GPIB-1014P User Manual 2-4 © National Instruments Corporation
Section Two