Chapter 3
Analog Output Timing/Control
DAQ-STC Technical Reference Manual
3-122
©
National Instruments Corporation
3.8.4 Interrupt Control
The analog output contains the hardware necessary for generating software interrupts based
on several conditions. The interrupt programming is accomplished using the
Interrupt_B_Enable_Register and the Second_Irq_B_Enable_Register. Interrupts remain
active until cleared by software. Interrupts can occur under the following conditions—overrun
error, START1, BC_TC, UC_TC, FIFO condition, UPDATE, and UI2_TC.
Table 3-8 summarizes the analog output interrupts along with the condition that causes the
interrupt.
3.8.5 Error Detection
The DAQ-STC can detect error conditions that occur during the analog output operation.
There are three primary analog output errors—overrun, BC_TC, and BC_TC trigger, and one
secondary analog output error—UI2_TC error.
3.8.5.1 Overrun Error
An overrun error occurs when an UPDATE command is issued to a DAC that was not loaded
with data. In hardware, this is detected when an UPDATE pulse occurs before all of the
TMRDACWR pulses from the previous UPDATE have completed. The TMRDACWR pulses
from the previous UPDATE may not have completed for several reasons, such as interference
from CPU writes to the DACs, an UPDATE interval that is too short, or a FIFO empty
condition that delays TMRDACWR.
Table 3-8.
Analog Output Interrupts
Interrupt
Condition
Error Interrupt
Interrupt generated on the detection of an overrun error condition.
START1 Interrupt
Interrupts are generated on valid START1 triggers received by the
DAQ-STC. A valid START trigger is one that is received while the BC
counter is armed and in the WAIT1 state.
BC_TC Interrupt
Interrupts are generated on the trailing edge of BC_TC.
UC_TC Interrupt
Interrupts are generated on the leading edge of UC_TC.
FIFO Interrupt
Interrupt generated on the FIFO condition indicated by the
AO_FIFO_Mode bitfield.
UPDATE Interrupt
Interrupts are generated on the trailing edge of UPDATE.
UI2_TC Interrupt
Interrupts are generated on the trailing edge of UPDATE2.