AC37 High-Speed Communication Adapter Card
EXTERNAL INTERRUPT LINE,
REMOTE I/O IRQ
The IRQ lines on the Phoenix connector are a bi-directional RS-485 link which are normally set as inputs. They are
meant to be used with the IRQ output lines found on Remote I/O bricks. The IRQ outputs of Remote I/O bricks are
RS-485 drivers which are held in tri-state mode until an interrupt is requested, at which time the outputs are
enabled and set active. The AC37 will receive this signal and set the IRQ Line Status bit in the Modem Status
Register. If enabled, this will cause a modem status interrupt to be generated.
The G4INT jumper group is provided to allow the external interrupt to be routed to a unique host CPU interrupt
request line. This may be necessary if communications software cannot implement the use of a ‘Clear To Send’
interrupt as the external (Remote I/O) interrupt handler. By installing a jumper in the G4INT group, and disabling the
modem status interrupt in the Interrupt Enable Register, the user may utilize separate interrupt request lines (with
unique vectors and routines) for the serial communications and external interrupt handling. The G4INT jumper will
directly route the external interrupt signal to the selected interrupt request line, and it may only be enabled or
disabled by the interrupt controller of the host AT. If used, only one jumper should be installed in the G4INT group,
and the user should be certain that the interrupt request line selected is not used by any other device, including the
IRQ GROUP selection.
Before a Remote I/O brick can generate an interrupt, a number of commands must be executed. These are:
1.
Set Event Table Entry
An entry must be made instructing the I/O brick to monitor for a specific event occurrence.
2.
Enable Event Table Entry
The event entry must be enabled for scanning by the I/O brick.
3.
Set Event Interrupt Status
The event entry interrupt must be enabled.
4.
Set System Options
The Global Interrupt Enable bit must be set.
And, of course, the event being monitored must then occur.
An interrupt from a Remote I/O brick is cleared by executing a ‘Read and Clear Event Latches’ command. All event
entries on a specific brick which are set to generate an interrupt should be specified when reading and clearing as
the interrupt output is cleared by the command.
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CHAPTER 3
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