71m6521be Maxim Integrated Products, Inc., 71m6521be Datasheet - Page 27

• Manufacturer Part Number: 71m6521be
• Description: Energy Meter Ic
• Manufacturer: Maxim Integrated Products, Inc.

Table 23 specifies the combinations of operation modes allowed for timer 0 and timer 1:
Timer/Counter Mode Control register (PCON):
The SMOD bit in the PCON register doubles the baud rate when set.
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.
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
PCON.7
Bit
Note: It is recommended to use the hardware watchdog timer instead of the software watchdog timer.
MSB
SMOD
Symbol
SMOD
Timer 0 - mode 0
Timer 0 - mode 1
Timer 0 - mode 2
--
Function
© 2005-2008 TERIDIAN Semiconductor Corporation
--
Table 25: PCON Register Bit Description
Table 24: The PCON Register
--
Table 23: Timer Modes
Not allowed
Mode 0
YES
YES
--
--
Not allowed
Timer 1
Mode 1
YES
YES
--
Energy Meter IC
Mode 2
--
YES
YES
YES
LSB
71M6521BE
DATA SHEET
JANUARY 2008
Page: 27 of 97