ADUC824 Analog Devices, ADUC824 Datasheet - Page 46

• Manufacturer Part Number: ADUC824
• Description: Precision Analog Microcontroller: 1MIPS 8052 MCU + 8kB Flash + 16/24-Bit ADC + 12-Bit DAC
• Manufacturer: Analog Devices

Specifications of ADUC824

• Mcu Core: 8052
• Mcu Speed (mips): 1
• Sram (bytes): 256Bytes
• Gpio Pins: 34
• Adc # Channels: 4

ADuC824
WATCHDOG TIMER
The purpose of the watchdog timer is to generate a device reset or
interrupt within a reasonable amount of time if the ADuC824
enters an erroneous state, possibly due to a programming error,
electrical noise, or RFI. The Watchdog function can be disabled by
clearing the WDE (Watchdog Enable) bit in the Watchdog Control
(WDCON) SFR. When enabled; the watchdog circuit will generate
a system reset or interrupt (WDS) if the user program fails to set
the watchdog (WDE) bit within a predetermined amount of time
WDCON
SFR Address
Power-On Default Value
Bit Addressable
Bit
7
6
5
4
3
2
1
0
P
R
E
3
Name
PRE3
PRE2
PRE1
PRE0
WDIR
WDS
WDE
WDWR
P
R
E
2
Watchdog Timer Prescale Bits
The Watchdog timeout period is given by the equation: t
Watchdog Status Bit
Watchdog Write Enable Bit
Watchdog Timer Control Register
C0H
10H
Yes
Description
(0 ≤ PRE ≤ 7; f
PRE3
0
0
0
0
0
0
0
0
1
PRE3–0 > 1001
Watchdog Interrupt Response Enable Bit
If this bit is set by the user, the watchdog will generate an interrupt response instead of a system
reset when the watchdog timeout period has expired. This interrupt is not disabled by the CLR
EA instruction and it is also a fixed, high-priority interrupt. If the watchdog is not being used to
monitor the system, it can alternatively be used as a timer. The prescaler is used to set the timeout
period in which an interrupt will be generated. (See also Note 1, Table XXXIV in the Interrupt
System section.)
Set by the Watchdog Controller to indicate that a watchdog timeout has occurred.
Cleared by writing a ‘0’ or by an external hardware reset. It is not cleared by a watchdog reset.
Watchdog Enable Bit
Set by user to enable the watchdog and clear its counters. If this bit is not set by the user within
the watchdog timeout period, the watchdog will generate a reset or interrupt, depending on WDIR.
Cleared under the following conditions, User writes ‘0,’ Watchdog Reset (WDIR = ‘0’); Hardware
Reset; PSM Interrupt.
To write data into the WDCON SFR involves a double instruction sequence. The WDWR bit must
be set and the very next instruction must be a write instruction to the WDCON SFR.
e.g.,
P
R
E
1
Table XVII. WDCON SFR Bit Designations
PRE2
0
0
0
0
1
1
1
1
0
CLR
SETB
MOV
SET B
PLL
P
= 32.768 kHz)
R
PRE1
0
0
1
1
0
0
1
1
0
EA
WDWR
WDCON, #72h
EA
E
0
(see PRE3–0 bits in WDCON). The watchdog timer itself is a
16-bit counter that is clocked at 32.768 kHz. The watchdog
time-out interval can be adjusted via the PRE3–0 bits in WDCON.
Full Control and Status of the watchdog timer function can be
controlled via the watchdog timer control SFR (WDCON). The
WDCON SFR can only be written by user software if the double
write sequence described in WDWR below is initiated on every
write access to the WDCON SFR.
W
D
I
R
PRE0Timout Period (ms) Action
0
1
0
1
0
1
0
1
0
;
;
;
;
15.6
31.2
62.5
125
250
500
1000
2000
0.0
disable interrupts while writing
to WDT
allow write to WDCON
enable WDT for 2.0s timeout
enable interrupts again (if rqd)
W
D
S
WD
= (2
PRE
Reset or Interrupt
Reset or Interrupt
Reset or Interrupt
Reset or Interrupt
Reset or Interrupt
Reset or Interrupt
Reset or Interrupt
Reset or Interrupt
Immediate Reset
Reserved
W
× (2
D
9
E
/f
PLL
))
W
D
W
R