Stand-Alone, 10-Channel, 10-Bit System Monitors

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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 chan-

nel 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 3FF hex to disable upper threshold

faults in unipolar mode, and 1FF hex in temperature or

bipolar mode. The power-up/reset default is 3FF 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 200 hex to disable lower threshold

faults in unipolar mode, or to 200 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

MAX1153/MAX1154 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 MAX1153/MAX1154 in automatic scan mode, set

the scan mode bit B2 in the setup register to logic 1.

In automatic scan mode, the MAX1153/MAX1154 con-

vert all enabled channels starting with the internal tem-

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 MAX1153/

MAX1154 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 MAX1153/MAX1154 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

MAX1153/MAX1154 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/differen-

tial, or unipolar/bipolar), carry out the following steps to