71M6521DE Datasheet, PDF (28/107 Pages) Teridian Semiconductor Corporation – Energy Meter IC

71M6521DE/DH/FE Data Sheet
Table 24 specifies the combinations of operation modes allowed for timer 0 and timer 1:
Timer 0 - mode 0
Timer 0 - mode 1
Timer 0 - mode 2
Mode 0
YES
YES
Not allowed
Timer 1
Mode 1
YES
YES
Not allowed
Mode 2
YES
YES
YES
Table 24: Timer Modes
Timer/Counter Mode Control register (PCON):
MSB
SMOD
--
--
--
--
--
--
Table 25: The PCON Register
The SMOD bit in the PCON register doubles the baud rate when set.
LSB
--
Bit
PCON.7
Symbol
SMOD
Function
Baud rate control.
Table 26: 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. It is strongly discouraged to use the software WDT.
Page: 28 of 107
Rev 2