M306N5FCTFP Renesas Electronics America, M306N5FCTFP Datasheet - Page 110

• Manufacturer Part Number: M306N5FCTFP
• Description: IC M16C MCU FLASH 100QFP
• Manufacturer: Renesas Electronics America
• Series: M16C™ M16C/6Nr

Specifications of M306N5FCTFP

• Core Processor: M16C/60
• Core Size: 16-Bit
• Speed: 20MHz
• Connectivity: CAN, I²C, IEBus, SIO, UART/USART
• Peripherals: DMA, WDT
• Number Of I /o: 87
• Program Memory Size: 128KB (128K x 8)
• Program Memory Type: FLASH
• Ram Size: 5K x 8
• Voltage - Supply (vcc/vdd): 4.2 V ~ 5.5 V
• Data Converters: A/D 26x10b; D/A 2x8b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 100-QFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -

M16C/6N Group (M16C/6N5)
Rev.2.40
REJ09B0011-0240
11. Watchdog Timer
The watchdog timer is the function of detecting when the program is out of control. Therefore, we recommend
using the watchdog timer to improve reliability of a system. The watchdog timer contains a 15-bit counter
which counts down the clock derived by dividing the CPU clock using the prescaler. Whether to generate a
watchdog timer interrupt request or apply a watchdog timer reset as an operation to be performed when the
watchdog timer underflows after reaching the terminal count can be selected using the PM12 bit in the PM1
register. The PM12 bit can only be set to 1 (watchdog timer reset). Once this bit is set to 1, it cannot be set to
0 (watchdog timer interrupt) in a program. Refer to 5.3 Watchdog Timer Reset for details about watchdog
timer reset.
When the main clock, on-chip oscillator clock or PLL clock is selected for CPU clock, the divide-by-n value for
the prescaler can be selected to be 16 or 128. If a sub clock is selected for CPU clock, the divide-by-n value
for the prescaler is always 2 no matter how the WDC7 bit is set. The period of watchdog timer can be
calculated as given below. The period of watchdog timer is, however, subject to an error due to the prescaler.
With main clock, on-chip oscillator clock or PLL clock selected for CPU clock
Watchdog timer period =
With sub clock selected for CPU clock
Watchdog timer period =
For example, when CPU clock = 16 MHz and the divide-by-n value for the prescaler = 16, the watchdog timer
period is approx. 32.8 ms.
The watchdog timer is initialized by writing to the WDTS register. The prescaler is initialized after reset. Note
that the watchdog timer and the prescaler both are inactive after reset, so that the watchdog timer is
activated to start counting by writing to the WDTS register.
In stop mode, wait mode and hold state, the watchdog timer and prescaler are stopped. Counting is resumed
from the held value when the modes or state are released.
Figure 11.1 shows the Watchdog Timer Block Diagram. Figure 11.2 shows Registers WDC and WDTS.
Figure 11.1 Watchdog Timer Block Diagram
CM07 : Bit in CM0 register
WDC7 : Bit in WDC register
PM12 : Bit in PM1 register
PM22 : Bit in PM2 register
Apr 14, 2006
CPU clock
HOLD
Internal RESET signal
("L" active)
page 88 of 372
Write to WDTS register
Prescaler
Prescaler dividing (16 or 128) ✕ Watchdog timer count (32768)
Prescaler dividing (2) ✕ Watchdog timer count (32768)
1/128
1/16
1/2
On-chip oscillator clock
CM07 = 0
WDC7 = 0
CM07 = 0
WDC7 = 1
CM07 = 1
PM22 = 1
CPU clock
PM22 = 0
CPU clock
Watchdog timer
Set to
7FFFh
PM12 = 0
Watchdog timer
Interrupt request
PM12 = 1
Watchdog timer
Reset
11. Watchdog Timer