General-Purpose Timing Signal Connections And General-Purpose Counter/Timing Signals; Figure 3-13. Extupdate* Signal Timing For Updating Dac Output; Figure 3-14. Extupdate* Signal Timing For Generating Interrupts - National Instruments Low-Cost Multifunction I/O Board for ISA Lab-PC+ User Manual

Signal Connections
EXTUPDATE*
DAC OUTPUT
UPDATE
CNTINT
DACWRT

Figure 3-13. EXTUPDATE* Signal Timing for Updating DAC Output

Since a rising edge on the EXTUPDATE* signal always sets the CNTINT bit in the Status
Register, the EXTUPDATE* signal can also be used for periodic interrupt generation timed by
an external source. The CNTINT bit is cleared by writing to the Timer Interrupt Clear Register.
Figure 3-14 illustrates a timing sequence where EXTUPDATE* is being used to generate an
interrupt.
EXTUPDATE*
CNTINT
TMRINTCLR

Figure 3-14. EXTUPDATE* Signal Timing for Generating Interrupts

The following rating applies to the EXTCONV*, EXTTRIG and EXTUPDATE* signals.
Absolute maximum voltage input rating: -0.5 to 7.0 V with respect to DGND

General-Purpose Timing Signal Connections and General-Purpose Counter/Timing Signals

The general-purpose timing signals include the GATE, CLK, and OUT signals for the three
8253(B) counters. The 8253 Counter/Timers can be used for general-purpose applications such
as pulse and square wave generation; event counting; and pulse-width, time-lapse, and frequency
Lab-PC+ User Manual
t ext
t ext Minimum 50 nsec
3-24 © National Instruments Corporation
Chapter 3