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參數(shù)資料
| 型號： | CCU3000 |
| 廠商： | MICRONAS SEMICONDUCTOR HOLDING AG |
| 元件分類： | 微控制器/微處理器 |
| 英文描述： | Central Control Unit |
| 中文描述： | MICROCONTROLLER, PQCC68 |
| 封裝： | PLASTIC, LCC-68 |
| 文件頁數(shù)： | 19/77頁 |
| 文件大?。?/td> | 837K |
| 代理商： | CCU3000 |
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CCU 3000, CCU 3000-I
CCU 3001, CCU 3001-I
MICRONAS INTERMETALL
19
2.14. Watchdog
– not active after Reset
– activated when written, cannot be stopped via soft-
ware
– to retrigger, the watchdog period negated bit by bit
must be rewritten within the preset space of time (first
write event is also counted)
– triggers reset, the software can identify if Reset was
generated by watchdog
– 16 ms to 4 s time-out for 4 MHz system clock
This counter circuit offers hardware support for software
problems. It is disabled after reset and enabled with the
first write of the desired time value into its register. The
value to program is calculated by
n = T
WD
* f
system
/ 65536 – 1
with n = watchdog counter value to be programmed for
T
WD
= the desired watchdog time and
f
system
= system frequency.
Remarks:
a) To prevent the generation of a ‘RESET’ by the watch-
dog before it could be retriggered by the software,
watchdog counter values less than 2 should not be pro-
grammed
b) The system clock as input of the watchdog counter is
influenced by the system clock prescaler, determining
the CPU speed (register addr. 200 H).
Software can’t stop this counter but has to retrigger it by
writing the inverted value (one’s complement) of the pre-
ceding written pattern into its register, which makes un-
wanted retrigger loops of disturbed software unlikely.
These writes have to occur within the time frame (8 ms
to 2 s at 8 MHz system clock), defined with the first write.
If no write with the expected pattern occurs within the
programmed time period, the watchdog circuit resets the
CCU at the end of the time period. There will also be a
watchdog reset if another pattern is written instead of the
expected one. The software can detect if a reset was
generated by the watchdog: Bit 0 of the watchdog regis-
ter is ‘0’ if the last reset was generated by the watchdog.
This bit is reset only with an external reset, e.g. gener-
ated by power-on.
Examples:
To set a cycle time of 1 second with 8 MHz system clock
the value is 121. This value is calculated as follows:
system frequency: 8 MHz
watchdog cycle time:
65536 / 8 MHz = 8.192 ms,
counter value:
1 s / 8.192 ms = 122.07.
The nearest integer value is 122. Because a 0 loaded
into the counter divides by 1, already, the watchdog
counter has to be programmed with
122-1 = 121.
With
the formula above
n = 121 = 1s * 8 MHz/65536 – 1
The software sequences in Assembler could look like
this:
Definitions:
;constants:
WATCHDOG_TIME
;CCU I/O–address:
watchdog_address
;variable:
watchdog_value
EQU
121
EQU
202H
EQU
; of free RAM location)
30H ;(address
Example 1:
During initialization the watchdog is filled with the de-
sired time-value:
LDA
STA
STA
#WATCHDOG_TIME
watchdog_address
watchdog_value
;memorize
; watchdog pattern
In the main loop of the program the watchdog has to be
retriggered cyclically:
LDA
EOR
STA
STA
watchdog_value
#FFH
watchdog_address
watchdog_value
;invert bits
;memorize new
; watchdog pattern
Example 2:
If an interrupt function occurs cyclically, one value may
be programmed in the interrupt service routine, while the
other is written in the main loop. So both the continuity
of executing the interrupt service and the main loop are
checked:
During initialization the watchdog shadow variable is
filled with the desired time-value:
LDA
STA
#WATCHDOG_TIME
watchdog_value
;memorize
; watchdog pattern
Sequence in the interrupt function:
LDA
CMP
BEQ
;
STA
EOR
STA
SKIP_IRQ_WD
watchdog_value
#WATCHDOG_TIME
SKIP_IRQ_WD
watchdog_address
#$FF
watchdog_value
...
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| CCU3000-I | Central Control Unit |
| CCU3001 | Central Control Unit |
| CCU3001-I | Central Control Unit |
| CD-700-KAC-GAB-XX.XXX | Complete VCXO Based Phase Lock Loop |
| CD-700-LAF-GGB-XX.XXX | Complete VCXO Based Phase Lock Loop |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| CCU3000I | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Microcontroller |
| CCU3000-I | 制造商:MICRONAS 制造商全稱:MICRONAS 功能描述:Central Control Unit |
| CCU3001 | 制造商:MICRONAS 制造商全稱:MICRONAS 功能描述:Central Control Unit |
| CCU3001I | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Microcontroller |
| CCU3001-I | 制造商:MICRONAS 制造商全稱:MICRONAS 功能描述:Central Control Unit |
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