PIC16F877A Timer0 delay problem?

[gstekboy]

To get min .5ms delay. I chosen prescalar as 1:32 (The main frequency chosen as 4Mhz), what will be the TMR0 register value? Is it 0x64 or 0x63 !!

 

[esp1]

hi,
A 4MHz crystal will give an internal clock of 1MHz, ie: 1uSec Period.
pre-scaling by 32 will give a 32uSec Period.

So Tmr0 is 8Bit, ie:256 max, but 0.5mSec/32uSec = decimal 15.625.!!

Check your calculations.
E

 

[gstekboy]

hi,
A 4MHz crystal will give an internal clock of 1MHz, ie: 1uSec Period.
pre-scaling by 32 will give a 32uSec Period.

So Tmr0 is 8Bit, ie:256 max, but 0.5mSec/32uSec = decimal 15.625.!!

Check your calculations.
E

Sorry it is 5ms.

So whether I need to chose ox63 or ox64 for TMR0 reg.

 

[betwixt]

Nearest is 64 (decimal) which gives you 4.992mS.

If you use 63 the period will be 5.024mS which has much larger error.

If you want exactly 5mS use TMR1 pre-loaded with 60536 (0xEC78) and 1:1 prescaler.

Brian.