Chapter 2
Analog Input Timing/Control
©
National Instruments Corporation
2-5
DAQ-STC Technical Reference Manual
Figure 2-2 shows a simplified model of the AITM module.
Figure 2-2.
AITM Simplified Model
One of the primary features of the AITM is that a wide variety of signals can be selected as
timing and control sources. The simplified model depicts this as a select circuit, which
chooses between the 10 PFI signals PFI<0..9>, the seven RTSI signals
RTSI_TRIGGER<0..6>, and the dedicated STOP input signal AI_STOP_IN. Many of the
signals required for the ADC can come from external sources routed through the selector. The
DAQ-STC can also generate the timing sources internally.
The simplified model in Figure 2-2 shows that the source for the CONVERT pulse may come
from the SI2 counter (internal CONVERT source) or the select circuit (external CONVERT
source). SOC (start of conversion) and EOC (end of conversion) are status signals generated
by the ADC. SOC indicates that a conversion has begun and EOC indicates that a conversion
is complete.
Using CONVERT as a reference, the output circuit generates several ancillary signals used
on the board. The LOCALMUX_CLK (configuration FIFO advance) signal, which pulses
after an integral number of CONVERTs, advances the configuration FIFO to the next input
channel. The LOCALMUX_FFRT (configuration FIFO retransmit) signal, which pulses
when the configuration FIFO empties, refills the configuration FIFO. The EXTMUX_CLK
(external multiplexer clock) signal, which pulses on every CONVERT, advances the channel
multiplexer. The SHIFTIN signals (AI_FIFO_SHIFTIN and SHIFTIN), which pulse after the
ADC has completed a conversion, move the data into the analog input data FIFO. The
AIFREQ (AI data FIFO request) signal generates a DMA request based on the analog input
PFI<0..9>
RTSI_TRIGGER<0..6>
AI_STOP_IN
SOC
EOC
GHOST
AIFFF
AIFHF
AIFEF
SELECT
CONTROL
STOP
START
START1
SC_TC
SI2_TC
SI_TC
DIV_TC
SI2
COUNTER
SI
COUNTER
DIV
COUNTER
SC
COUNTER
OUTPUT
CONVERT
AI_FIFO_SHIFTIN
SHIFTIN
LOCALMUX_CLK
LOCALMUX_FFRT
EXTMUX_CLK
SCAN_IN_PROG
AIFREQ
