Maxim Integrated 71M6534 Energy Meter IC Family Software - Manual (Page 103)

71M653X Software User’s Guide
5.18.10 Real Time Clock Compensation
The real-time clock compensation is very different from the 652x series. Fixed rate adjustments are nonvolatile and
automatic, so that they continue when the MPU is not operating.
The 32 KHz crystal rate can be measured precisely in the factory by using a precision frequency counter to measure
the 1 second or 4 second output from the TMUX pin. During this measurement, the RTCA_ADJ register should be set
to the middle of its range, 0x40, and PREG and QREG should be set to the middle of their range.
After this, the capacitance driving the crystal can be adjusted by have the meter software write and preserve a value for
the real time clock analog adjustment, RTCA_ADJ XDATA 0x2011.
After RTCA_ADJ is set, the clock rate can be remeasured using the frequency counter with TMUX.
In operation the clock’s rate can be digitally adjusted for temperature or to follow the line frequency by adjusting the
PREG and QREG registers. These are actually a single register that adds or subtracts a count after a certain number
of counts.
Setting PREG and QREG to zero will cause the seconds register to count at ½ Hz, rather than 1 Hz.
5.18.11 Battery Modes
The battery modes strongly resemble the 6521. In particular, the RAM is unpowered in sleep and LCD-only mode.
In the 653X the LCD registers are also unpowered in sleep mode to save power.
The 653x has 8 bytes of nonvolatile RAM, GP0..GP7. At this time, in A01 and A02 versions of the IC, GP0..7 are
cleared at reset, but remain unchanged in battery modes. Later versions may preserve these register in reset.
In the 653x, fixed-rate clock compensation is in hardware and continues to run in sleep mode. Code is not needed to
compensate the clock when leaving sleep mode.
The 653x sleep mode consumes less than 1 microamp, far better than the 6521.
5.18.12 Watchdog Reset
In the 653x, the watchdog reset is equivalent to the reset pin. So, after a watchdog reset, the 653x does not require
reinitialization to a reset state, and the 6521 did.
5.18.13 Temperature Compensation
When operating with “internal” temperature compensation, the 71M653X uses MPU-based temperature compensation
similar to the 6521 for the metering.
The real time clock’s temperature compensation is also MPU-based, but has a different algorithm, because it must set
the hardware rate register.
v1.1v1.1 TERIDIAN Proprietary 103 of 116
© Copyright 2005-2008 TERIDIAN Semiconductor Corporation