PIC Timing with servo

[Lockhead]

Hi,

I have written a basic program controlling five rc servo and basically the program works for pic16F877a. But when I am changing PIC, some PIC results in no movement at the servo (I'm trying PIC16F1826).

I thought that, by minor modification on the header & fuses relate to the timing then the program will work exactly the same regarding on frequency oscillator. When I trace the program, function "delay_ms(1)" only gives me 250ns instead of 1 miliseconds. (simulation by proteus).

I've tried LP,XT,HS,EC FUSES but none seems working with freq 20Mhz and 32Mhz. I've also tried the same program structure with MPLAB but yield the same result. Nevertheless, I'm planning to build the hardware soon to verify whether it is just bug in my proteus simulation or is it something wrong with my program flow.

1) Is it just a bug in simulation that the program will work on the hardware?
2) Based on this experience, I'm not sure on how reliable is the delay_ms() and delay_us() function when cmpared to other PIC in the same 8-bit family?
3) Moreover, does internal and external oscillator provide significant degree of accuracy?
4) Currently my program are based on delay_ms() and delay_us() function. Should I used cycle count instead of timing count?
5) From what I have read, for controlling simultaneous multiple servo I have to use timer interrupt right? Advice me on the program structure

... Sorry for the long post

[temtronic]

from my experience..

1) NEVER ever trust Proteus. It's a piece of 'junkware'. I could expand on that but really, just delete from your PC.

2)The delay_functions are very good and have worked fine for me during the past 2 decades. I've never needed nanosecond timing, so maybe others can reply with actual numbers.

3)The internal oscillator is not 'stable' compared to an external crystal or external oscillator. While 'fine' for simple, non time critical projects, you'll get better results using a crystal and 2 caps, best results from an external oscillator in a 'can'.

4)delay_ms(xxx) and delay_us(yyy) MUST be completed before the PIC will do anything else so on all but the simplest projects it's best to use a 'timer based' ISR to control the program.

5)Yes, better to use ISR for your servo controlling. There are several ways to do it. Though with RC servos you don't have any feedback, making the program much easier to write.

hth
jay