PBP projects for R/C models

[Kenjones1935]

I copied your code snip from POST #73 at 3:02 on the 28th of January.

I noticed in the .asm code that it wanted to:

INCLUDE "MACKRA~1.MAC"

There is no such file in my computer. Do I need a copy? May I have one?

Also the compiler complained that:

Error 118: "Overwriting previous address contents (2007)

Page 157 of DS33014K says that Error 118 occurred because "Code was previously generated for this address" I assume it is talking about address (2007). I do not see where in the .asm code this is happening. I do not even know what to look for.

Ken

[Kenjones1935]

Mackrackit,

From what I understand your code will do a PWM every time TMR0 overflows.

What I need to do is make this overflow happen every 20ms. That is 50 pulses per second. We have a 4 meg oscillator. If I were designing this counter I think I would have it set to 20,000 each time it overflows. I gather from page 74 of the Data Sheet that this is not possible. The biggest prescaler is 256.

How about a routine that counts these interrupts until 1/50 of a second has elapsed then calls PWM? I would have it send one pulse out pin 1 with the duty as defined by "duty". It would look like

PWM 1,duty,1

I have found a section on Timers in a book called Running Small Motors with PIC Microcontrollers that has an example of MicroEngineering Labs code that makes an eight digit LCD display the time in hours, minutes and seconds. I think this code must do something like I need.

Ken

[rmteo]

You want 20,000 counts before it overflows. Setting the prescaler to 1:256, you will need 20,000/256 counts = 78. The counter rolls over (overflows and sets T0IF) when it reaches 255, so if you pre-load it with 255-78 = 177, then it will overflow approximately every 20mS.

[mackrackit]

Mackrackit,
From what I understand your code will do a PWM every time TMR0 overflows.

The code in post #73 will toggle a LED when TMRO overflows. The LED on PORTD.7 will gradually become brighter then turn off and start over again.

This was just an example of an interrupt working with something else going on.

You do have to be careful with this as things will sometimes not work as expected. Like they say, the machine will do what it is told, not what you want

This is the same code as in post #73 with some modifications to demonstrate a "pitfall".
The START loop still has PORTD.7 PWMing the LED with PORTD.0 added to be toggled.
Inside of the interrupt loop the same PWM that is on PORTD.7 is now on PORTD.6.

What do you think will happen?
What does happen?

'16F887 INT RUPT
'44 PIN DEMO BOARD

 @ __config _CONFIG1, _INTRC_OSC_NOCLKOUT & _WDT_ON & _MCLRE_OFF & _LVP_OFF & _CP_OFF

 INTCON.5 = 1    'ENABLE TMR0  DATA SHEET SECTION 14.3.2
 OSCCON = %01110000 '8 Mhz
 OPTION_REG = %10000111  ' 1:256 PRESCALE
 ON INTERRUPT GOTO TLOOP
 CNT  VAR BYTE
 D    VAR BYTE
 D = 0
 HIGH PORTD.0
 PAUSE 500

 START:
 FOR CNT = 0 TO 150
 PWM PORTD.7,D,100
 D = D + 2
 NEXT CNT
 TOGGLE PORTD.0
 PAUSE 100
 GOTO START

 DISABLE
 TLOOP:
 INTCON.2=0 ' DATA SHEET SECTION 14.3.2
 TOGGLE PORTD.4
 FOR CNT = 0 TO 150
 PWM PORTD.6,D,100
 D = D + 2
 NEXT CNT
 RESUME
 ENABLE

[Kenjones1935]

Just like you said it would.

Now on to your next one. It compiles and works also. I see what it does. I need to figure out how.

Thank you!!

[Kenjones1935]

Can anyone point me to a definition of "prescaler".
What I thought it meant does not seem to jive with what I am seeing.

Ken

[Kenjones1935]

"Running Small Motors with PIC Microcontrollers" says, on page108

"A pre-scaler is applied to the system clock and affects the timer by slowing down the system clock as it applies to the timer. Normally the timer is fed by a fourth of the basic clock frequency, which is called Fosc/4. In a system running a 4 MHz the timer sees a clock running at 1 MHz. If the pre-scaler is set for 1:8, the clock will be slowed down by another eight times, and the timer will see a clock at 125kHz."

"The post-scaler setting determines how may overflows will go by before an interrupt is triggered."

If I pre-scale TMRO 1:256 I will get overflows at about 4K per second. If I add a post-scaler of 1:64 I will end up with about 62 interrupts per second.

Close enough for government work?

Ken

[Kenjones1935]

I just found in DS33023 section 11.6.

"There is only one pre-scaler available which is mutually exclusively shared between Timer 0 and Watchdog Timer."

So I have to count the 4000 Interrupts per second using a

FOR CNT To 80
NEXT

loop. That will give me much closer to 50 pulses per second.

Correct?

[mackrackit]

I copied your code snip from POST #73 at 3:02 on the 28th of January.
I noticed in the .asm code that it wanted to:
INCLUDE "MACKRA~1.MAC"
There is no such file in my computer. Do I need a copy? May I have one?

Looks like you have the code named MACKRACKIT?
The *.MAC file is the macro file generated by PBP. It will be in your project directory. The name is chopped to the 8.1? standards.

Also the compiler complained that:
Error 118: "Overwriting previous address contents (2007)
Page 157 of DS33014K says that Error 118 occurred because "Code was previously generated for this address" I assume it is talking about address (2007). I do not see where in the .asm code this is happening. I do not even know what to look for.

Ken

Looks like you are setting the configs in the *.inc file. I have them in the code. Just comment that line out and it should be OK.