Poll External Interrupt

Polls the external interrupt of the Q8 data acquisition system.

Library

qctools

Description

The Poll External Interrupt block for the Q8 series of I/O cards provides a mechanism for polling the external interrupt line, EXT_INT, of the card. It reads the Interrupt Status Register of the Q8 card. The output goes high when the external interrupt occurs. The block has an option for resetting the interrupt flag after an interrupt occurs. The block polls the Interrupt Status Register each sampling instant. The Poll Interrupts series of blocks may be used in Windows regardless of the status of the Q8 Windows driver.

This block may be used in slave Q8 cards to cause a watchdog reset when the watchdog of a master Q8 card expires. To do so, put a Watchdog block in the master with the "Enable external output" option checked. Then put Poll Exterrnal Interrupt blocks for the slave Q8 cards with the "EXT_INT acts as watchdog" option checked. Connect the WATCHDOG output of the master Q8 card to the EXT_INT lines of the slave Q8 cards.

Block Outputs

EXTINT

The output goes high when a rising or falling edge occurs on the EXT_INT line. The "EXT_INT polarity" option selects the active edge of the EXT_INT line.

Parameters and Dialog Box

Board Number

The board number of the I/O card. If there is only one Q8 board in your system, then the board number should be zero. The second Q8 board in your system is board number 1, etc.

Sample Time

A sample time must be specified for all discrete blocks. The default value extracts the sample time from the RTW Options dialog, under Solver/Fixed step size. A numeric value rather than 'auto' should be specified in this dialog field for this default to make sense.

EXT_INT Polarity

Polarity of the EXT_INT input. If this option is not checked then a falling edge on the EXT_INT input triggers the EXTINT output going high. Otherwise a rising edge is the trigger. The EXT_INT line has a pullup resistor to bring it high when the input is unconnected. Hence, this option is normally unchecked by default.

EXT_INT Acts as Watchdog

If this option is checked then an edge on the EXT_INT input causes the analog outputs to be reset and the digital I/O lines to be pulled high. This option is useful for connecting limit switches and emergency stop buttons to the Q8. It can also be used to have the watchdog timer of one Q8 board act as a watchdog for a whole set of Q8 boards. To do so, use a Watchdog block on the "master" with the "Enable external output" option enabled. Then use a Poll Interrupts, Poll External Interrupt or External Status block with the "EXT_INT acts as watchdog" option checked for the slave boards.

Clear Flag After Polling

When this option is checked, the block clears the polled bit of the Interrupt Status Register after reading it. This option allows the flag to be repeatedly polled. The output will remain high for one sampling instant when this option is checked. Otherwise, the output stays high once it has gone high.