SM39R08A5 Datasheet, PDF (32/58 Pages) SyncMOS Technologies,Inc – Additional Baud Rate Generator

SM39R08A5
8-Bit Micro-controller
with 8KB Flash
& 256B RAM embedded
Once the watchdog is started it cannot be stopped. User can refreshed the watchdog timer to zero by writing 0x55 to
Watch Dog Timer refresh Key (WDTK) register. This will clear the content of the 8-bit counter and let the counter re-start
to count from the beginning. The watchdog timer must be refreshed regularly to prevent reset request signal from
becoming active.
When Watchdog timer is overflow, the WDTF flag will set to one and automatically reset MCU. The WDTF flag can be
clear by software or external reset or power on reset.
23KHz RC
oscillator
Clear
1. Power on reset WDTF = 0
2. External reset
3. Software write “0”
WDTF
Set WDTF = 1
TAKEY
(55, AA, 5A)
1
2^WDTM
WDTM[3:0]
WDTC
Enable WDTC
write attribute
WDTEN
WDTCLK
Enable/Disable
WDT
WDT
Counter
Refresh
WDT Counter
WDT
time-out
select
CWDTR = 0
WDT time-out
reset
WDT time-out
CWDTR = 1 Interrupt
WDTK
(0x55)
Fig. 8-1: Watchdog timer block diagram
Mnemonic Description Direct
TAKEY
Time Access
Key register
F7h
Watchdog
WDTC timer control B6h
register
Watchdog
WDTK timer refresh B7h
key
RSTS
Reset status
register
A1h
Bit 7
-
-
Bit 6 Bit 5 Bit 4
Watchdog Timer
Bit 3
TAKEY [7:0]
CWDT
R
WDTE
-
Bit 2 Bit 1
WDTM [3:0]
WDTK[7:0]
-
-
PDRF WDTF SWRF LVRF
Bit 0 RST
00H
04H
00H
PORF 00H
Mnemonic: TAKEY
7
6
5
4
3
2
TAKEY [7:0]
Address: F7h
1
0
Reset
00H
Watchdog timer control register (WDTC) is read-only by default; software must write three specific
values 55h, AAh and 5Ah sequentially to the TAKEY register to enable the WDTC write attribute. That is:
MOV TAKEY, #55h
MOV TAKEY, #AAh
MOV TAKEY, #5Ah
Specifications subject to change without notice contact your sales representatives for the most recent information.
ISSFD-M067
Ver E SM39R08A5 06/30/2015
- 32 -