参数资料
型号: EVAL-ADUC7122QSPZ
厂商: Analog Devices Inc
文件页数: 88/96页
文件大小: 0K
描述: BOARD EVALUATION FOR ADUC7122
设计资源: EVAL-ADUC7122 Schematic
ADUC7122 Gerber Files
ADUC7122 BOM
标准包装: 1
系列: MicroConverter® ADuC7xxx
类型: MCU
适用于相关产品: ADUC7122
所含物品:
ADuC7122
Rev. 0 | Page 89 of 96
TIMER3—WATCHDOG TIMER
08
755
-03
8
16-BIT
LOAD
TIMER3
VALUE
16-BIT
UP/DOWN
COUNTER
PRESCALER
1, 16, OR 256
LOW POWER
32.768kHz
TIMER3 IRQ
WATCHDOG
RESET
Figure 37. Timer3 Block Diagram
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.
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
Description
T3CON
The configuration MMR.
T3LD
6-bit registers (Bit 0 to Bit15); holds 16-bit unsigned
integers.
T3VAL
6-bit registers (Bit 0 to Bit 15); holds 16-bit unsigned
integers. This register is read only.
T3ICLR
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.
Table 164. Timer3 Load Register
Name
Address
Default Value
Access
T3LD
0xFFFF0360
0x03D7
R/W
This 16-bit MMR holds the Timer3 reload value.
Table 165. Timer3 Value Register
Name
Address
Default Value
Access
T3VAL
0xFFFF0364
0x03D7
R
This 16-bit, read-only MMR holds the currentTimer3 count value.
Table 166. Timer3 Clear Register
Name
Address
Default Value
Access
T3CLRI
0xFFFF036C
0x00
W
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
Address
Default Value
Access
T3CON
0xFFFF0368
0x00
R/W
once
only
The 16-bit MMR configures the mode of operation of Timer3 as
is described in detail in Table 168.
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