WDT values

nazoa · Joined: 09 Feb 2007 Posts: 58

Hello,

I am using the 18F4550 and need to know the timeout values for the watchdog timer. I know the available fuses are wdt1, wdt2, ...wdt128. Also the data sheet tells me that the timeout can be set between 4ms and 132s. However, I am not sure how to relate the fuse settings to an actual value.

Can anyone explain? My PIC is running at 48MHz and I need a timeout between 5s and 10s.

Thanks.

Ttelmah · Guest

Read section 25.2 in the data sheet.
This chip, has a much better watchdog, than most other chips, offering quite stable timings. The nominal period is 4mSec, which is then extended by the possible postscalers (1:1 - 1:32768). The WDT bits in the fuses, set this postscaler. The available values, are the 'binary' counts (1 2 4 8 etc.)
So, 5/0.004 = 1250, while 10/0.004= 2500. The only binary value between these, is 2048. This will give a nominal 2048*0.004 seconds (8.192). Use WDT2048 to get this.

Best Wishes