External Status

Returns the status of the EXT_INT input of the Q8 data acquisition system.

Library

qctools

Description

The External Status block for the Q8 series of I/O cards provides a mechanism for checking the status of the EXT_INT input of the card. The block queries the EXT_INT bit of the Status Register each sampling instant. Note that unlike the Interrupt Status Register, the status flags are not latched. The Status series of blocks may be used in Windows regardless of the status of the Q8 Windows driver.

Block Outputs

EXTINT

The output reflects the state of the EXT_INT line. This bit is not affected by EXT_INT polarity options. Hence, this bit of the Status Register may be used to treat the EXT_INT line as an extra digital input.

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. This option does not actually affect the EXT_INT status flag, but it does affect the operation of EXT_INT as a watchdog input (see the "EXT_INT acts as watchdog" option below). 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.