WDT timer on the PIC16F687

[M3GAPL3X]

wdt timer

Hi guys,

In the spec sheet, it says that the WDT has a:
Time-out period is from 1 ms to 268 seconds

I can't figure out how this is true with the given post-scalar values of the WDT timer.

Here are the values of WDTCON:


WDTPS<3:0>: Watchdog Timer Period Select bits
Bit Value = Prescale Rate
0000 = 1:32
0001 = 1:64
0010 = 1:128
0011 = 1:256
0100 = 1:512 (Reset value)
0101 = 1:1024
0110 = 1:2048
0111 = 1:4096
1000 = 1:8192
1001 = 1:16384
1010 = 1:32768
1011 = 1:65536
1100 = reserved
1101 = reserved
1110 = reserved
1111 = reserved


If anyone can tell me how I can get 1 ms or 268 seconds from those values, it would be greatly appreciated! The 18f series was more straight forward.

In the spec sheet it says that Enhanced Low-Current Watchdog Timer (WDT)
with On-Chip Oscillator (Software selectable
nominal 268 Seconds with Full Prescaler) with
Software Enable

 

[GSM Man]

set timer pic16f687

That's because it allows you to use the Timer0 prescaler as an 8-bit WDT post-scaler - see the path highlighted in red on the attached image.

 

[M3GAPL3X]

pic16f687

Thanks GSM for your patience. That charge really helped!