C8051F220 Silicon Laboratories Inc, C8051F220 Datasheet - Page 94

• Manufacturer Part Number: C8051F220
• Description: IC 8051 MCU 8K FLASH 48TQFP
• Manufacturer: Silicon Laboratories Inc
• Series: C8051F2xxr

Specifications of C8051F220

• Core Processor: 8051
• Core Size: 8-Bit
• Speed: 25MHz
• Connectivity: SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, WDT
• Number Of I /o: 32
• Program Memory Size: 8KB (8K x 8)
• Program Memory Type: FLASH
• Ram Size: 256 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 3.6 V
• Data Converters: A/D 32x8b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 48-TQFP, 48-VQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -

C8051F2xx
Disable WDT
Writing 0xDE followed by 0xAD to the WDTCN register disables the WDT. The following code segment
illustrates disabling the WDT.
The writes of 0xDE and 0xAD must occur within 4 clock cycles of each other, or the disable operation is
ignored. Interrupts should be disabled during this procedure to avoid delay between the two writes.
Disable WDT Lockout
Writing 0xFF to WDTCN locks out the disable feature. Once locked out, the disable operation is ignored
until the next system reset. Writing 0xFF does not enable or reset the watchdog timer. Applications alays
intending to use the watchdog should write 0xFF to WDTCN in their initialization code.
Setting WDT Interval
WDTCN.[2:0] control the watchdog timeout interval. The interval is given by the following equation:
For a 2.0 MHz system clock, this provides an interval range of 32msec to 524msec. WDTCN.7 must be
written as 0 when setting this interval. Reading WDTCN returns the programmed interval. WDTCN.[2:0] is
111b after a system reset.
94
Bits7–0: WDT Control
Bit4:
Bits2–0: Watchdog Timeout Interval Bits
CLR
MOV
MOV
SETB
R/W
Bit7
EA
WDTCN,#0DEh
WDTCN,#0ADh
EA
Writing 0xA5 both enables and reloads the WDT.
Writing 0xDE followed within 4 clocks by 0xAD disables the WDT.
Writing 0xFF locks out the disable feature.
Watchdog Status Bit (when Read)
Reading the WDTCN.[4] bit indicates the Watchdog Timer Status.
0: WDT is inactive
1: WDT is active
The WDTCN.[2:0] bits set the Watchdog Timeout Interval. When writing these bits,
WDTCN.7 must be set to 0.
R/W
Bit6
4
SFR Definition 12.1. WDTCN: Watchdog Timer Control
3+WDTCN[2:0]
R/W
Bit5
; disable all interrupts
; disable watchdog timer
;
; re-enable interrupts
x T
SYSCLK
R/W
Bit4
, (where T
Rev. 1.6
R/W
Bit3
SYSCLK
is the system clock period).
R/W
Bit2
R/W
Bit1
R/W
Bit0
SFR Address:
Reset Value
xxxxx111
0xFF