PBP projects for R/C models

[ScaleRobotics]

Hey Ken, you can either take the serial out, or change it a bit. Here is one to use a slower baudrate, without using the baudcon.3 setting.

DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
DEFINE HSER_SPBRG 64 ' 19200 Baud @ 20MHz, 0.16%
DEFINE HSER_CLROERR 1 ' Clear overflow automatically

I use a program from Mister E, called Mister E PIC Multi-Calc that spits all these above settings out after you pic a baud rate. Pretty cool! http://www.picbasic.co.uk/forum/show...9&postcount=38

Sometimes PIC chips can be a pain because the newer chips will move things around on us. So when we try to learn a different chip, or upgrade to a different part, things do not work without a bit of leg work.

I was using a PIC18F2520, which had a register called T0CON for adjusting the Timer0 or TMR0. That sounds like it makes sense. However, on the PIC16F887 that you are using, the same Timer0 TMR0 is adjusted by using .... the Option Register. Not quite making as much sense, is it.

Anyway.... HOW do I know this? Answer: I do not. I have to look up both data sheets for each of those pic chips, and compare them. Not all 375 pages, but just whatever portions I think are giving me trouble. In this case, the Timer0. Then I have to see that everything that is set in the PIC18F2520 for the timer, is set for the PIC16F887. Then I will probably have to do the same thing for the other timers. AND, it will probably not work when I first try it, because I will probably miss something.

So, looking at page 77 of your data sheet, and page 125 of my data sheet, lets see what we can screw up, I mean "test".

Well I had it set to:

TMR0ON - off
T08Bit - configured as a 16 bit timer (this could be a problem)
T0CS - Internal instruction cycle clock
T0SE - increment on low to high transition of clock pin
PSA - use prescaler selection bits
T0PS - 1:4 prescaler selection bits

Now lets see what we have for the Option register...
Well, looking at the data sheet, your chip's T0 is only 8 bit, but if we are lucky, we will just have lower resolution. Timer0 is the time base for creating a servo pulse out from 1 to 2 ms.

Option_Reg
RBPU - Port B pull ups (nothing to do with timer) probably leave off - 1
INTEDG - Nothing to do with timer
T0CS - keep at 0 like above
T0SE - keep at 0 like above
PSA - keep at 0 like above
PS - we can start at 001 like above, but we might have to change things up since this
is not a 16 bit timer.....If I was smarter about how these worked, I could mathematically figure this out.....

Now, how do we start this timer0, because it looks like bit 7 is NOT going to do this for us...

To be continued .....

[boroko]

Scalerobotics,

Bravo! very well laid out explanation (well at least part one). That is the kind of stuff that drives newbees nuts and makes them give up in frustration. There is no easy place to learn it if you don't have a mentor. Patient, concise, and relevant. Nice job.

Bo

[Kenjones1935]

I awoke this morning looking out my window onto eight new inches of wind packed snow. Plenty of time to think.

What scalerobotics said makes sense to me. In 1957 I was programming the AN/FSQ-7 SAGE Air Defense computer. We worked in machine language. It took us years to develop and distribute a symbol and subroutine library sufficient to allow us to focus on the radar data reading, intercept calculating algorithms needed to accomplish air defense. Building this subroutine library was a big task. The architecture of the machine did not change.

This morning I said to myself, "Back to basics." It may have been a mistake for me to purchase PICbasic PRO. Without being able to tap into the developments of others on the 16F88x structure, I may be better off in ASM. That way I will be forced back to basics.

This world of microprocessors reopens the academic importance of old fashioned "computer science". I was afraid that we had become too product oriented to care what is a "register".

I have two PIC books:
PIC PROJECTS by Parchizadeh and Vuksanovic
and
RUNNING SMALL MOTORS WITH PIC MICROCONTROLLERS by Sandhu

Seems like I should cease dreaming of getting a prototype to blink in sync with a PWM input signal and get back to the books. I've got plenty of time. Did I mention that we are snowed in without an all wheel drive car?

Ken

[ScaleRobotics]

This morning I said to myself, "Back to basics." It may have been a mistake for me to purchase PICbasic PRO. Without being able to tap into the developments of others on the 16F88x structure, I may be better off in ASM. That way I will be forced back to basics.

This world of microprocessors reopens the academic importance of old fashioned "computer science". I was afraid that we had become too product oriented to care what is a "register".
Ken

Ken, I hope I did not discourage, for it was my intent to encourage. But back to basics is always a good idea, no matter what path you choose. For PIC devices, it can be a difficult task to transfer a program from one type of device to another.

A better place to start on the learning curve, might be to use Darrel Taylors interrupt code examples, and try to get the interrupt blinking led going on your device. Then try to modify it in some way that is closer to the end product you want. In that way, it forces you to learn about different registers, but only a few at a time. Here is Darrels blinky example. http://darreltaylor.com/DT_INTS-14/blinky.html

Joe had some great advice. In trouble shooting, it is always helpful to figure out what parts of the code DO work. I always like using the serial port to help tell me what is happening in the device, and to check register values, etc.

Let us know how we can help you.

Walter

[Kenjones1935]

I got Darrel Taylor's blinky to work on my PICkit 2 16F887. I had to change the output pin to the LED to match the printed circuit on the 44 pin demo board.

Now I would like to get blinky to interrupt on the rising edge and the falling edge of a signal coming in CCP1 which is RC2.

Darrel Taylor's blinky contains this line

@ INT_ENABLE TMR1_INT ; enable Timer 1 interrupts

Where do I look for the definition of INT_ENABLE? I used SEARCH. I had no luck at all.

Ken

[ScaleRobotics]

That's a great start Ken!

INT_ENABLE is a Darrel Taylor command for his DT_INTS. This is the same as enabling, or disabling a certain interrupt. To set up CCP interrupts, you first add a line like my code had:

INT_Handler   CCP1_INT,      PWMeasure,   ASM,  yes

Then enable it:
@ INT_ENABLE CCP1_INT

But you will also have to configure it. Make portc.2 an input. And configure your CCP1
CCP1CON = %00000101 ;capture every rising edge

Now I used Chuck's code to do the capture. It needs the sub16.inc include file to be included, and we will need some variables like

risetime var word      ;used for pulse width measure start of pw
falltime var word      ;time at end of pulse width
falltime_l var falltime.byte0
falltime_h var falltime.byte1
risetime_l var risetime.byte0
risetime_h var risetime.byte1

asm
PWMeasure

    BTFSS   CCP1CON, CCP1M0 ; Check for falling edge watch
    GOTO    FALL_EDGE       ; Go pick up the falling edge
    MOVF    CCPR1L,W        ; else store leading edge value
    MOVWF   _risetime_l         ; into 16 bit word risetime
    MOVF    CCPR1H,W
    MOVWF   _risetime_h
    BCF     CCP1CON, CCP1M0 ; Now capture the trailing edge
    GOTO    ISR_2           ; Exit the interrupt service routine
        
FALL_EDGE:
    BSF     CCP1CON, CCP1M0 ; Re-set for trailing edge capture
    MOVF    CCPR1L,W        ; Store the captured value into
    MOVWF   _falltime_l         ; falltime_l and ...
    MOVF    CCPR1H,W
    MOVWF   _falltime_h       ;             ... falltime_h
    ;
    ; 16 bit subtract 
    ;     falltime = falltime - risetime
    ;
    SUB16   _falltime, _risetime
ISR_2
    INT_RETURN

endasm

Now, if you read the data sheet, you see in 11.1 Table 11-1 that capture mode uses timer1. So you will have to set this. Looks like it may be same settings as I have in T1CON. This will also start the timer. It runs continuously, and we don't care about interrupts on T1. We just want to read the timer at interrupt high edge of CCP1, and read timer on low edge of pulse. Then we should have a value present at falltime, representing the length of the pulse.

[Kenjones1935]

I did not expect this project to be so discombobulating.

Thanks to this forum's help, I think I will get it.

ken