71M6521BE
Energy Meter IC
DATA SHEET
JANUARY 2008
Table 23 specifies the combinations of operation modes allowed for timer 0 and timer 1:
Timer 1
Mode 0
YES
Mode 1
YES
Mode 2
YES
Timer 0 - mode 0
Timer 0 - mode 1
Timer 0 - mode 2
YES
YES
YES
Not allowed
Not allowed
YES
Table 23: Timer Modes
Timer/Counter Mode Control register (PCON):
MSB
LSB
SMOD
--
--
--
--
--
--
--
Table 24: The PCON Register
The SMOD bit in the PCON register doubles the baud rate when set.
Bit
Symbol
Function
PCON.7
SMOD
Table 25: PCON Register Bit Description
WD Timer (Software Watchdog Timer)
The software watchdog timer is a 16-bit counter that is incremented once every 24 or 384 clock cycles. After a reset, the
watchdog timer is disabled and all registers are set to zero. The watchdog consists of a 16-bit counter (WDT), a reload register
(WDTREL), prescalers (by 2 and by 16), and control logic. Once the watchdog is started, it cannot be stopped unless the
internal reset signal becomes active.
Note: It is recommended to use the hardware watchdog timer instead of the software watchdog timer.
WD Timer Start Procedure: The WDT is started by setting the SWDT flag. When the WDT register enters the state 0x7CFF,
an asynchronous WDTS signal will become active. The signal WDTS sets bit 6 in the IP0 register and requests a reset state.
WDTS is cleared either by the reset signal or by changing the state of the WDT timer.
Refreshing the WD Timer: The watchdog timer must be refreshed regularly to prevent the reset request signal from becoming
active. This requirement imposes an obligation on the programmer to issue two instructions. The first instruction sets WDT and
the second instruction sets SWDT. The maximum delay allowed between setting WDT and SWDT is 12 clock cycles. If this
period has expired and SWDT has not been set, the WDT is automatically reset, otherwise the watchdog timer is reloaded with
the content of the WDTREL register and the WDT is automatically reset. Since the WDT requires exact timing, firmware needs
to be designed with special care in order to avoid unwanted WDT resets.
TERIDIAN strongly discourages the use of the software WDT.
V1.0
© 2005-2008 TERIDIAN Semiconductor Corporation
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