Interrupt & device setup for a PIC16F628A in Microcode Studio Plus

[Acetronics2]

Hi, PiKachu

I think reading carefully the '628a datashhet, Chapter CCP, sub chapter CAPTURE could greatly :

1) improve your knowlege
2) show you you're re-inventing the wheel
3) solve your timing headache.

May be your reflected signal input will have to be directed to PortB.3 ... but I do not think it will be an unavoidable problem ...


Now, ... you have a PbP command called RCTime with a 2µs @ 20Mhz resolution ... ( see manual for how it works !!! )

2*1E-6 * 330 = .66 E-3 m ... no comment !
2*65535*1E-6*330 = 43.25 m ... more than your sensors could ever sense !!!


... and remember all period measurements also can be done like that ...

wish you happy hours

Alain

[wildpikachu]

@ skimask. yeah i know but we make do with what we have.

@acetronics: I chose BR0/INT because the receiving circuit is a single frequency passband filter, with a peak at 40.3kHz and the -3db points at 39.2kHz and 41.6kHz, which is then connected to a comparator giving me a change of 0VDC-5VDC hence wanting to use the external interrupt on a change of PORTB.0, I'm using the RB3/CCP to generate a 40kHz signal.
I'm aiming for a range of 0.5m to 20m but with the attenuation on a 40kHz signal in air 10m is more realistic, if only i could get my hands on a 25kHz transducer set (they dont bring them into south africa).

ok think i've got my timer1 problems sorted. wanting a prescaler value of 1:2, a preset value of 1000. is the following code right?


preset Var Word
preset = 1000 ' to give me a preset value of 2ms at a prescaler value of 1:2 for timer1
TMR1H = preset.highbyte
TMR1L = preset.lowbyte
T1CON = %00010000 'prescaler value of 1:2, timer diabled
INTCON = %11010000 ' GIE & PEIE & INTE enabled
PIE1.0 = 0 ' TMR1 interrupt disabled
PIR1.0 = 0 ' TMR1 interrupt flag reset

start code......
........
.......
T1CON.0 = 1 ' timer1 enable with a preset value of 1000 and a prescaler value of 1:2
pause 2000 'wait 2 seconds, this is the only place that the external interrupt must be active, still working on that tho.
T1CON.0 = 0 ' timer 1 disable
more code....
.........
.........
end code

i've read through the datasheet and it doesnt explain GIE and PEIE very well, what is their purpose? does GIE enable every interrupt or just allow the enabled interrupts to happen throughout the entire program? do i have to set PEIE to enable an external interrupt?

[Archangel]

. . . if only i could get my hands on a 25kHz transducer set (they dont bring them into south africa) . . .

I have got to ask . . . why not?

[wildpikachu]

Hi JoeS.

No one brings them into South Africa, not even RS components, and its going to cost about double the entire project to ship one over so its not worth it just for an estimated 5meter distance gain and my lecturer has told me that i will get 100% if i can measure up to 10 meters with 5% accuracy because its more about implementing the theory than actual long distance measuring ability. I can always change it later, 2 lines of code and 4 resistors on the filter.

[Acetronics2]

@acetronics: I chose BR0/INT because the receiving circuit is a single frequency passband filter, with a peak at 40.3kHz and the -3db points at 39.2kHz and 41.6kHz, which is then connected to a comparator giving me a change of 0VDC-5VDC hence wanting to use the external interrupt on a change of PORTB.0, I'm using the RB3/CCP to generate a 40kHz signal.
I'm aiming for a range of 0.5m to 20m but with the attenuation on a 40kHz signal in air 10m is more realistic, if only i could get my hands on a 25kHz transducer set (they dont bring them into south africa).

ok think i've got my timer1 problems sorted. wanting a prescaler value of 1:2, a preset value of 1000. is the following code right?


preset Var Word
preset = 1000 ' to give me a preset value of 2ms at a prescaler value of 1:2 for timer1
TMR1H = preset.highbyte
TMR1L = preset.lowbyte
T1CON = %00010000 'prescaler value of 1:2, timer diabled
INTCON = %11010000 ' GIE & PEIE & INTE enabled
PIE1.0 = 0 ' TMR1 interrupt disabled
PIR1.0 = 0 ' TMR1 interrupt flag reset

start code......
........
.......
T1CON.0 = 1 ' timer1 enable with a preset value of 1000 and a prescaler value of 1:2
pause 2000 'wait 2 seconds, this is the only place that the external interrupt must be active, still working on that tho.
T1CON.0 = 0 ' timer 1 disable
more code....
.........
.........
end code

i've read through the datasheet and it doesnt explain GIE and PEIE very well, what is their purpose? does GIE enable every interrupt or just allow the enabled interrupts to happen throughout the entire program? do i have to set PEIE to enable an external interrupt?

Hi, Pikachu

I see you have locked your hardware definition ... so, let's try to do with.

in your code, you forget to enable TMR1 INT ( PIE1) when using TMR1 ... you can enable it in your header, if TMR1 just works during your 2s Pause.

PEIE is intended to control PERIPHERALs interrupts such from Timer1, ADC, COMP ( ~ External modules )...

GIE controls ALL interrupts wherever they come ... AND, of course, allow them IF they are individually allowed ...

Alain

[wildpikachu]

Hi Alain.
thanks for the reply, really cleared things up for me. I wasnt going to use timer1 to generate an interrupt but have decided to let it now. I'm using a simple repeated check on RB0 to check for a change instead of using an interrupt.

I've attached my code, seems right to me but if anyone finds any problems or has any advice please let me know.

Cheers
Guy

[Acetronics2]

Hi, Picatchu

nice code template ... easy to read !

some tricks :

  if (PORTB.0 = rb0old) then goto changetest ' If there is no change then test again

change for :

While (PORTB.0 = rb0old)
Wend

this will loop till a change occurs ... ( much faster ! )

Note here I did not understand why use the "change" feature : from your explanations ... if "back" signal detected, it simply turns PortB.0 input ON ( ... or OFF depending Hardware)

    dummy = (time((6 * temp)+ 3300))    ' calculate part of the full calculation

to me ( I can fail ...)
it might be :

    dummy = (time*((6 * temp)+ 3300))    ' calculate part of the full calculation

By the Way : Speed of sound in air = SQR ( 13 * 287* (273.15 + Temp) /10 )

... @ sea level ...

...

Alain

PS: May be you could try a "samples" request here ...

http://www.midascomponents.co.uk/

[wildpikachu]

Hi alain.

thanks for the "while" and maths suggestions and for the complement on my code, I will implement them. the checking for a change on RB0 is because the receiving circuit is set to be extremely sensitive and I am not sure what state the comparator, that is connected to RB0, will be in (either 0V or 5V) thats why i'm checking for a change so that regardless of what state the comparator is initially i will stop timer1 as soon as possible. if the code was this: if PORTB.0 = 1 and initially the comparator was at a high i would get an instant stop without even receiving a signal. well in my mind it makes sence :-)

The calculation is got from one of my physics books and modified it to get rid of any decimal places and to work the distance out in one. it uses temperature in celcius rather than Kelvin.

thanks for the link, lets see if they are willing to send overseas :-)

Cheers and thanks again for the help!

- Guy