ADUC7122 Analog Devices, ADUC7122 Datasheet - Page 89

• Manufacturer Part Number: ADUC7122
• Description: Precision Analog Microcontroller, 12-Bit Analog I/O, ARM7TDMI® MCU
• Manufacturer: Analog Devices

Specifications of ADUC7122

• Mcu Core: ARM7 TDMI
• Mcu Speed (mips): 40
• Sram (bytes): 8192Bytes
• Gpio Pins: 32
• Adc # Channels: 13

TIMER3—WATCHDOG TIMER
Timer3 has two modes of operation: normal mode and
watchdog mode. The watchdog timer is used to recover from an
illegal software state. Once enabled, it requires periodic
servicing to prevent it from forcing a reset of the processor.
Timer3 reloads the value from T3LD either when Timer3
overflows or immediately when T3ICLR is written.
Normal Mode
The Timer3 in normal mode is identical to Timer0 in 16-bit
mode of operation, except for the clock source. The clock source
is the 32.768 kHz oscillator and can be scaled by a factor of 1,
16, or 256. Timer3 also features a capture facility that allows
capture of the current timer value if the Timer2 interrupt is
enabled via IRQEN[5].
Watchdog Mode
Watchdog mode is entered by setting T3CON[5]. Timer3 decre-
ments from the timeout value present in the T3LD register until
0. The maximum timeout is 512 seconds, using the maximum
prescalar/256 and full scale in T3LD.
User software should only configure a minimum timeout
period of 30 milliseconds. This is to avoid any conflict with
Flash/EE memory page erase cycles, requiring 20 ms to
complete a single page erase cycle and kernel execution.
If T3VAL reaches 0, a reset or an interrupt occurs, depending
on T3CON[1]. To avoid a reset or an interrupt event, any value
must be written to T3ICLR before T3VAL reaches zero. This
reloads the counter with T3LD and begins a new timeout
period.
Once watchdog mode is entered, T3LD and T3CON are write
protected. These two registers cannot be modified until a
power-on reset event resets the watchdog timer. After any other
reset event, the watchdog timer continues to count. The
watchdog timer should be configured in the initial lines of user
code to avoid an infinite loop of watchdog resets.
LOW POWER
32.768kHz
Figure 37. Timer3 Block Diagram
PRESCALER
1, 16, OR 256
COUNTER
UP/DOWN
TIMER3
VALUE
16-BIT
16-BIT
LOAD
WATCHDOG
RESET
TIMER3 IRQ
Rev. 0 | Page 89 of 96
Timer3 is automatically halted during JTAG debug access and
only recommences counting after JTAG has relinquished control
of the ARM7 core. By default, Timer3 continues to count during
power-down. This can be disabled by setting Bit 0 in T3CON. It is
recommended that the default value is used, that is, the watchdog
timer continues to count during power-down.
Timer3 Interface
Timer3 interface consists of four MMRS as shown in the table
below.
Table 163. Timer3 Interface Registers
Register
T3CON
T3LD
T3VAL
T3ICLR
Table 164. Timer3 Load Register
Name
T3LD
This 16-bit MMR holds the Timer3 reload value.
Table 165. Timer3 Value Register
Name
T3VAL
This 16-bit, read-only MMR holds the currentTimer3 count value.
Table 166. Timer3 Clear Register
Name
T3CLRI
This 8-bit, write-only MMR is written (with any value) by user
code to refresh (reload), Timer3 in watchdog mode to prevent a
watchdog timer reset event.
Table 167. Timer3 Control Register
Name
T3CON
The 16-bit MMR configures the mode of operation of Timer3 as
is described in detail in Table 168.
Description
The configuration MMR.
6-bit registers (Bit 0 to Bit15); holds 16-bit unsigned
integers.
6-bit registers (Bit 0 to Bit 15); holds 16-bit unsigned
integers. This register is read only.
8-bit register. Writing any value to this register clears
the Timer3 interrupt in normal mode or resets a new
timeout period in watchdog mode.
Address
0xFFFF0360
Address
0xFFFF0364
Address
0xFFFF036C
Address
0xFFFF0368
Default Value
0x03D7
Default Value
0x03D7
Default Value
0x00
Default Value
0x00
ADuC7122
Access
R/W
Access
R
Access
W
Access
R/W
once
only