SDA5523 Micronas Semiconductor, SDA5523 Datasheet - Page 64

• Manufacturer Part Number: SDA5523
• Description: SDA55xx TVText Pro
• Manufacturer: Micronas Semiconductor

SDA 55xx
Table 2–39: Maximum and minimum WDT overflow time period
Fig. 2–9: Block Diagram
2.10.7. WDT as General Purpose Timer
The watch dog timer WDT counter can be used as a
general purpose timer in timer mode. The associated
load register can be used either as load register or
independent scratch pad register for the programmer.
This is achieved by setting WDT_tmr bit.
WDT_tmr bit can only be set before starting the WDT
timer. Once the watchdog timer is started it is not pos-
sible to switch to general purpose timer mode.
If WDT_tmr bit is set then timer can be started using
WTmr_strt bit.
When the timer is started it
– Resets the WTmr_ov overflow flag.
– Loads the preload value from WDT_rel and starts
64
f
Min.
Max.
WDT
counting up.
f
33.33 MHz
33.33 MHz
system
WDT_Refresh
WDT_Rel
WDT_Ctrl
:128
:2
WDTREl_7
WDT_Ref
WDT_In
WDT_In
M
U
X
WDTREl_6
WDT_Start
WDT_Tmr
Sept. 10, 2004; 6251-556-3DS
WDT_in
0
1
WDT_Low
WDT_Ctrl
WDT_nARst
WDTREl_5
WTmr_Strt
WDT_Ref
WDTREl_4
WTmr_Ov
WDT_Rst
Upon overflow the WDT_rst bit is not set neither is
internal watchdog reset initiated. Overflow is indicated
by the bit WTmr_ov (r/w). Overflow also sets the inter-
rupt source bit CISR0 (WTmr). Both of these bits are
set by hardware and must be cleared by software. If
the corresponding watchdog timer interrupt enable IE1
(EWT) bit is set then upon overflow the interrupt is initi-
ated.
After an overflow the timer starts to count from
WDT_rel. It is possible for the microcontroller to stop
the timer by resetting the WTmr_strt bit any time.
While the timer is running, the WDT_tmr bit cannot be
toggled. Any write access to this bit is ignored. To reset
the WDT_tmr bit, either timer is stopped (WTmr_strt).
However it is possible to stop the timer (WTmr_strt)
and toggle the bit (WDT_tmr) with the same instruc-
tion.
WDT_High
WDT_Rel
WDTREl_3
8
WDT_rel
FF
00
--
--
H
H
WDTREl_2
---
---
WDT_Tmr
WDTREl_1
M
U
X
---
---
WTmr__Ov/Int
WDT_Rst
WDTREl_0
---
---
P
184.3 µs
3.02 s
WDT
DATA SHEET
Micronas