MAX1253 Datasheet, PDF (22/29 Pages) Maxim Integrated Products – Stand-Alone, 10-Channel, 12-Bit System Monitors with Internal Temperature Sensor and VDD Monitor

Stand-Alone, 10-Channel, 12-Bit System Monitors
with Internal Temperature Sensor and V_DD Monitor
Upper Threshold Register
A conversion result greater than the value stored in the
upper threshold register results in a fault, increasing
the internal fault counter by one. When the fault count
exceeds the value stored in fault bits B7–B4 of the
channel configuration register, the channel’s alarm bits
in the alarm register are set, resulting in an interrupt on
INT.
The upper threshold register data format must be the
same as the input channel. When the input channel is
configured for single-ended or differential unipolar volt-
age measurements, data stored in the upper threshold
register is interpreted as straight binary. For input chan-
nels configured for temperature measurements or as
differential bipolar voltage inputs, the upper threshold
register data is interpreted as two’s complement. Load
the register with FFF hex to disable upper threshold
faults in unipolar mode, and 7FF hex in temperature or
bipolar mode. The power-up/reset default is FFF hex.
See the Command Word section on how to read/write
to the upper threshold registers.
Lower Threshold Register
Conversion results lower than the value stored in the
lower threshold register increment the internal fault
counter. Considerations about channel configuration
register fault bits B7–B4, INT interrupts, and data for-
mat are the same as for the upper threshold register.
Set the register to 000 hex to disable lower threshold
faults in unipolar mode, or to 800 hex in temperature or
bipolar mode. The power-up/reset default is 000 hex.
See the Command Word section on how to read/write
to the lower threshold registers.
Current Data Registers
The current data register holds the last conversion
result or the digitally averaged result, when enabled
(see the Averaging section). The current data registers
default to 800 hex at power-up/reset and can be read
from and written to through the serial interface. See the
Command Word section on how to read/write to the
current data registers.
INT Interrupt Output
INT provides an indication that an alarm has occurred
in the system. It can be programmed (see Table 9) to
operate as a push-pull digital output or as an open-
drain output (requiring either a pullup or a pulldown
resistor) for wired-OR interrupt lines. Bits B3 and B4 in
the setup register configure INT and determine its
response to an alarm event.
When an internal fault counter exceeds the threshold
stored in the fault bits (B7–B4) of the corresponding chan-
nel configuration register, the alarm bits for that particular
channel are updated to indicate an alarm. When any bit in
the alarm register is set, the INT output becomes active,
and stays active until all alarm bits are cleared. See the
Alarm Register section for more information.
Servicing Interrupts at INT
After detecting an interrupt on INT, the µC’s interrupt
routine should first read the alarm register to find the
source of the alarm and reset the alarm bits by using
any of the methods described in the Alarm Register
section. Then it can continue with any other action
required by the application to react to the alarm.
Note: Multiple alarm conditions can be present. The
INT remains active until all alarm conditions have been
cleared.
Performing Conversions
At power-up or after a RESET command, the
MAX1253/MAX1254 default to shutdown mode with all
channels enabled, set for single-ended voltage mea-
surements, and with the scan mode set to manual. Start
a conversion by issuing a manually triggered conver-
sion command with the address bits of the channel
selected (see the Manual Conversion section for more
details) or by setting automatic scan mode. To place
the MAX1253/MAX1254 in automatic scan mode, set
scan mode bit B2 in the setup register to logic 1.
In automatic scan mode, the MAX1253/MAX1254 con-
vert all enabled channels starting with the internal tem-
perature sensor, followed by the V_DD monitor, then by
AIN0 to AIN7. As the scan sequence progresses, the
analog inputs are converted and the resulting values
are stored for each channel into its current data regis-
ter. Once the scan cycle completes, the MAX1253/
MAX1254 wait a period determined by the sample wait
bits (B7, B6, B5) in the setup register and then repeat
the scan cycle.
After configuring the MAX1253/MAX1254 with automat-
ic scan mode enabled, the devices do not require any
intervention from the system µC until an alarm is trig-
gered. All conversion and monitoring functions can
continue running indefinitely.
Manual Conversion
In manual mode (scan mode bit in the setup register
set to zero, the default after power-up/reset), the
MAX1253/MAX1254 convert individual channels with
the Manually Triggered Conversion command.
Assuming that, either by power-up/RESET defaults or
by previous initialization, the channel to be addressed
is both enabled and configured for the type of signal to
be acquired (voltage/temperature, single ended/differ-
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