Datasheet

ADC
Window
Comparator
X
(2)
ULRx[7:0]
(2)
CounterX
ALMCNT[2:0]
(1)
LLRx[7:0]
UpperLimitThreshold
LowerLimitThreshold
Alarmfor
ChannelX
CHXData
ADS7924
SBAS482A –JANUARY 2010–REVISED MAY 2010 www.ti.com
ALARM When an alarm occurs, the INT pin can be configured
to generate an interrupt. The channel that generated
The ADS7924 offers an independent alarm function
the alarm can be read from the registers. A read of
for each input channel. An 8-bit window comparator
the Interrupt Control register clears the alarm register
can be enabled to test the ADC conversion result
and also resets the alarm counter.
against an upper limit set by the ULR register and
against a lower limit set by the LLR register. If the
ADC OPERATING MODES
conversion result is less than or equal to the LLR
threshold value or greater than or equal to the ULR
The ADS7924 offers multiple operating modes to
threshold value, the comparator is tripped. There are
support a wide variety of monitoring needs.
separate upper and lower registers for each input
Conversions can either be started manually or set to
channel.
automatically continue. The mode is set by writing to
the MODE register, and changes take effect as soon
A programmable counter determines how many
as the write completes. Table 2 gives a brief
comparator trips it takes to generate an alarm. A
description of each mode.
separate counter is used for each channel and is
incremented whenever the comparator trips, either for
Idle Mode
the upper or lower thresholds. That is, an ADC
conversion result on channel 1 that exceeds the ULR
Use this mode to save power when not converting. All
threshold or falls below the LLR threshold increments
circuits are shut down.
the counter for that channel. Figure 22 shows a
conceptual diagram of the window comparator and
Awake Mode
alarm circuitry.
All circuits are operating in this mode and the ADC is
ready to convert. When switching between modes, be
sure to first select the Awake mode and then switch
to the desired mode. This procedure ensures the
internal control logic is properly synchronized.
(1) The same ALMCNT value is used for all four window comparators.
(2) X = 0 to 3.
Figure 22. Window Comparator/Alarm Conceptual Block Diagram
Table 2. Mode Descriptions
MODE DESCRIPTION
Idle All circuits shutdown; lowest power setting
Awake All circuits awake and ready to convert
Manual-Single Select input channel is converted once
Manual-Scan All input channels are converted once
Auto-Single One input channel is continuously converted
Auto-Scan All input channels are continuously converted
Auto-Single with Sleep One input channel is continuously converted with programmable sleep time between conversions
Auto-Scan with Sleep All input channels are continuously converted with programmable sleep time between conversions
Auto-Burst Scan with
All input channels are converted with minimal delay followed by a programmable sleep time
Sleep
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