Motorola MVME172 - Manual (Page 94)

2-16 Computer Group Literature Center Web Site
VMEchip2
2
VMEbus Interrupter
The interrupter provides all the signals necessary to allow software to
request interrupt service from a VMEbus interrupt handler. The chip
connects to all signals that a VMEbus interrupter is required to drive and
monitor.
Requiring no external jumpers, the chip provides the means for software to
program the interrupter to request an interrupt on any one of the seven
interrupt request lines. In addition, the chip controls the propagation of the
acknowledge on the IACK daisy-chain.
The interrupter operates in the release-on-acknowledge (ROAK) mode.
An 8-bit control register provides software with the means to dynamically
program the status/ID information. Upon reset, this register is initialized to
a status/ID of $0F (the uninitialized vector in the 68K-based environment).
The VMEbus interrupter has an additional feature not defined in the
VMEbus specification. The VMEchip2 supports a broadcast mode on the
IRQ1 signal line. When this feature is used, the normal IRQ1 interrupt to
the local bus interrupter should be disabled and the edge-sensitive IRQ1
interrupt to the local bus interrupter should be enabled. All boards in the
system which are not participating in the broadcast interrupt function
should not drive or respond to any signals on the IRQ1 signal line.
There are two ways to broadcast an IRQ1 interrupt. The VMEbus
interrupter in the VMEchip2 may be programmed to generate a level one
interrupt. This interrupt must be cleared using the interrupt clear bit in the
control register because the interrupt is never acknowledged on the
VMEbus. The VMEchip2 allows the output of one of the tick timers to be
connected to the IRQ1 interrupt signal line on the VMEbus. When this
function is enabled, a pulse appears on the IRQ1 signal line at the
programmed interrupt rate of the tick timer.