SH3000 Datasheet, PDF (12/24 Pages) Semtech Corporation – Low-Power Programmable Multifunction Support IC for Microcontrollers

SH3000 MicroBuddy™
SYSTEM MANAGEMENT
Periodic Interrupt / Wakeup Timer
Simple and versatile, the Periodic Interrupt / Wakeup
Timer can be used to create very accurate recurring
interrupts for use by the host micro. With some
minimum software support from the host processor, it
can also be used to create alarms, with practically
unlimited duration.
While the timer is running, the host processor may
be halted, consuming no energy. The interrupt wakes
up the processor, which can perform the requisite task
and go back to sleep, until the next periodic interrupt.
This mode of operation can achieve extremely low
average power consumption.
A 32-bit counter clocked by 32.768 kHz, producing a
minimum interval of 30.5 µs and the maximum interval of
36.4 hours, creates the Timer.
After reset, the Timer is stopped until the new value
for the time interval is written into the 4-byte Time
Interval register. When the least significant byte (LSB) is
written, the whole value is moved to the Time Interval
latch, the counter is reset and starts to increment with
the 32 kHz clock.
When the 32-bit comparator detects a match, an
interrupt is generated and the counter is reset and starts
the next timing cycle.
Although the counter cannot be written to, the
current value from the counter can be read at any time.
The whole 32-bit value is loaded into the 32-bit Current
Timer Value latch when the least significant byte is read.
This prevents errors stemming from the finite time
between the readings of individual bytes of the current
value.
Auxiliary functions
Scratchpad RAM and ID number
Four (4) bytes of general-purpose RAM reside on
the SH3000. Immediately after reset, they are loaded
with the factory-programmed values in the OTP memory.
For a standard device these values are 0x00, 0x00,
0x00, 0x00. Unique serial numbers or other information
could be located there. Please contact the factory for
custom requirements.
Voltage Regulator
Pin VREG can be used as a nominal 2.20 V reference
voltage or a supply source for small loads (<2 mA). A
bypass capacitor may be necessary between this pin
and VSS if the load generates large current transients or
a low ripple reference is required.
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