Watch Dog Timer (wdt), 12F683 nanowatt prescalar setting

Douglas Richard · Joined: 08 Sep 2003 Posts: 49 Location: Concord NH

Just started playing with the watch dog timer on the 12F683. Data sheet says the time out can be set between 1ms and 268 seconds. Is this a typo? Has anyone ever used such a long time out in a product? Is WDTCON the only register needed to be modified or is there something else?

languer · Joined: 09 Jan 2004 Posts: 144 Location: USA

Never used this feature on the chip, but after reading the datasheet it should be possible.

Referring to Figure 12-9. The WDT will use the LFINTOSC (31kHz) as reference. From there it goes through a 16-bit Prescaler (÷32 through ÷65536), and can further be routed through a 7-bit prescaler (÷1 through ÷128) shared with TMR0 (8-bit if used for TMR0). So you could have a maximum divisor of 8388608 (23-bit) - pretty nifty.

Registers used (all summarized in Table 12-8):
WDTCON.7-0
OPTION.3-0 -> PSA, PS2, PS1, PS0
CONFIG.3