pic18f887 event timer

[cpayne]

I am using a PIC18F887 with the internal oscilator set @ 8MHz. I have a subroutine I need to fire off at a routine basis (nominally every 22ms although I want it a constant that I can tune). Can someone give me a crash course (with as much details so I don't have to ask a bunch of follow on dummy questions) on how I set this up as some sort of timer on an interupt, preferably without using assembly, but if that is the only way, I am willing to try. I have no available IO pins remaining if that matters. I am using no other interupts, but future versions may entail a serial interupt. I only want it to fire after a complete line is executed, which I think is by default, then return to the next line after it runs the routine. I suspect its fairly easy, but I am not sure where to start.

Thanks,
Charlie

[mackrackit]

http://www.picbasic.co.uk/forum/showthread.php?t=3251
Be sure to read the first eight post.

[cpayne]

OK. This looks good. Thanks.

I think the overkill blinking light is the right for me to use. I am unlear what to change to get timer 1 to fire off every 22ms.

I assume it starts with this seting
T1CON = $31 ; Prescaler = 8, TMR1ON

I have two different harware setups I am trying to put it in. Both use the PIC16F887, one with an external 20MHz Osc, the other with an internal 8MHz. It looks like a prescaler of 1:8 is the max, so I suspect I need to do a counter in the interupt routine that only fires my event every nth time to acheive the 22ms event? Is this a big burden or is there a simpler way? Can someone show me some examples of how to do the math to get the event to fire off properly with the two oscillator speeds?


Thanks,
Charlie

[aratti]

Can someone show me some examples of how to do the math to get the event to fire off properly with the two oscillator speeds?

Charlie, play with the attached little tool to find out.

How to use it: click on the box enter the new value and press enter.

Cheers

Al.

[mackrackit]

Timer 1 is 16 bit.
At 8 Mhz with a prescale of 1 and a peload of 21537 will give 22.0 mSec
At 20 Mhz with a prescale of 2 and a peload of 10536 will give 22.0 mSec

http://www.picbasic.co.uk/forum/cont....-PICMultiCalc
http://www.picbasic.co.uk/forum/show...3259#post23259

[cpayne]

I am not sure if I shoudl reply to this thread or the main interupt thread.

Anyways, I am getting errors when compiling. It looks like its all with the includes files.

I have attached a screenshot showing the errors and my code

Can anyone let me know what I am doing wrong?

Thanks,
Charlie

[Darrel Taylor]

The answers are in the errors. They tell you what you need to do.

[cpayne]

...perhaps the errors mean something to those who know, but I am not smart enough to know (hence the reason I am for asking for help). A little more guidance would be appreciated. am I suposed to edit pbppic14.lib, if so how and where, its a huge file. Or am I suposed to change the includes file for the PIC16F887?

Thanks,
Charlie

[Darrel Taylor]

Add ...

wsave VAR BYTE $70 SYSTEM

to your program.

[cpayne]

OK. Thanks, Compiles now and have a blinking LED. Back to the timing... Sorry I am so dense with this.

How do I go about setting the timer for prescale of 1 and a peload of 21537

I have been looking at previous posts and the datasheet for the 16f887, but not really sure what I need to do.

I assume I have to set T1CON and perhaps OPTION_REG

Also would I be better off using Timer2 since its 8bit (would it be less resources, etc?). As the timer is tripping along, there is no issue with timing of other things like serial commands, I2C timing, etc?

[mackrackit]

http://www.picbasic.co.uk/forum/show...7472#post17472
Has the example to set the pre-scaler.
Then in your code for the pre-load.

PreLoad     VAR WORD
PreLoad =  21537 
TMR1L = PreLoad.LowByte
TMR1H = PreLoad.HighByte

Then in the interrupt routine

TMR1L = PreLoad.LowByte   ' Load the timer with preload value.
TMR1H = PreLoad.HighByte

Maybe....

[cpayne]

cool. I had it in the begining, did not have it in the interupt. Firing every 22ms on the scope.

So, this will not mess up anything as far as I2C or serial? or is that dependent on what I do during the interupt? (The final interupt will take about 10-14ms and fire off every 22ms)

[mackrackit]

So, this will not mess up anything as far as I2C or serial? or is that dependent on what I do during the interupt? (The final interupt will take about 10-14ms and fire off every 22ms)

You need to get in and out of an interrupt routine as quick as possible.
So if the I2C and serial stuff is handled out side then you should be good.

[cpayne]

In order to get in and out quick I will need to use another timer I guess. I need to fire off serries of 8 pulses every 22ms. The high pulses will range from 400us to 1800us with a 400uslow pulse/pause between each one. So I am looking for some advise as to the best approach. Would be the best approach it with a second timer or the same one? I guess if I use the same one I can add up all the small pulses and then wait the difference of 22ms and repeat, but I am not sure if that is as reliable as using two timers, perhaps simpler though. If two timers, should I use timer1 (the 16 bit one for the shorter pulses since their accuracty is more critical than the 22ms) and timer0 or timer2 for the 22ms event. Is there any big deal with changing the preload value for the shorter pulses each time?

In either approach, can I use a case select inside the interupt routine to remember where I am in the interupt pulse train each time I return, or is there something I have to do to pass variables in and out of the interupt routine.

Thanks,
Charlie

[mackrackit]

I probably worded that wrong. Just make sure you finish before the next period and/or leave enough time to do whatever else you need to do.

[cpayne]

I have finished puting the original non interupt code into the new program. any reason why PORTB.2 is all of a sudden reading high all the time. I can ground it out with a switch and it will not change state. I when back to the old program and the pin funtions fine, so I assume its something to do with the new interupt, since that is all that has changed, but I can't figure out what. Any suggestions. Thanks

[mackrackit]

Just for giggles can you post your current code? Preferably in code tags...

[cpayne]

here is the entire front end...

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

OSCCON = $70 'sets the oscillator speed
DEFINE OSC 8 'Oscillator speed in MHz

'http://www.picbasic.co.uk/forum/showthread.php?t=3251
INCLUDE "DT_INTS-14.bas"     ' Base Interrupt System
INCLUDE "ReEnterPBP.bas"     ' Include if using PBP interrupts

PORTA = %00000000 ' output logic at power-up
PORTB = %00000000 ' output logic at power-up
PORTC = %00000000 ' output logic at power-up
PORTD = %00000000 ' output logic at power-up
PORTE = %00000000 ' output logic at power-up

' Set up serial UART
define HSER_RCSTA 90H           ' Set Receive Status and control register
DEFINE HSER_TXSTA 24H           ' set transmit status and control register
DEFINE HSER_BAUD 19200          ' baud setting   19200  115200
define HSER_CLROERR 1           ' reset on serial buffer overflow

' Define Analog parameters
ADCON1 = %10000000          'Right Justify
ANSEL = %11111111           'Analog on for AN0-AN7
ANSELH = %00000000          'AN8-13 off

Define	ADC_BITS 10 	    ' Set number of bits in result
Define	ADC_CLOCK 3	        ' Set clock source (3=rc)
Define	ADC_SAMPLEUS 10	    ' Set sampling time in uS

' Alias pins  (0=Output, 1=Input)
L1      VAR PORTC.5 :TRISC.5 = 0
L2      VAR PORTD.2 :TRISD.2 = 0
L3      VAR PORTD.1 :TRISD.1 = 0
L4      VAR PORTD.0 :TRISD.0 = 0
L5      VAR PORTC.1 :TRISC.1 = 0

Sp      var PORTC.2 :TRISC.2 = 0  'pulsed signal 

S2      var PORTD.5 :TRISD.5 = 1 'mode switch - LCD Select Mode
S3      var PORTD.4 :TRISD.4 = 1 'mode switch - LCD Light 
S1      var PORTD.7 :TRISD.7 = 1 'mode switch - Plus 
S5      var PORTD.6 :TRISD.6 = 1 'mode switch - Minus 

S8      var PORTB.4 :TRISB.4 = 1 'Pelco-D board - Zoom
S11     var PORTB.5 :TRISB.5 = 1 'Peclo-D board - Zoom

S7      var PORTB.1 :TRISB.1 = 1 'RC board - Mast
S10     var PORTB.3 :TRISB.3 = 1 'RC board - Mast

S6      var PORTB.2 :TRISB.2 = 1 'Video Select

'Define RAM
i               var     byte
j               var     byte
RC_Mode         var     Bit  'Flag to switch back and forth from arm and drive funtions
S2_Rel          var     BIT  'flag to see if switch is realsed
S6_Rel          var     BIT  'flag to see if switch is realsed
Mode_Debug      var     bit  'Flag for LCD Debug Mode
Mode_Debug1     var     bit  'Flag for LCD Debug Mode
LCD_msg         var     byte 'Counter to reset LCD message Display
wsave           VAR     BYTE $70 SYSTEM 'value required for interupt
PreLoad         VAR     WORD 'Preload value for timer interupt
PreLoad =  21537 

JOY1X           var     word    ' Analog Values
JOY1Y           var     word
JOY2X           var     word
JOY2Y           var     word
P1              var     word
Battery         var     word    ' Battery voltage analog
Battery_r       var     word    ' battery voltage remainder
Batt_div        con     660     ' scaling value to get Volts
Batt_Alarm      con     480     ' approx 7.2V
Batt_Stop       con     430     ' approx 6.5V
Batt_stop1      var     byte
Batt_beep       var     byte
Lights_Last     var     BIT
Video_Mode      var     BYTE
Video_Changed   VAR     BYTE

JOY1X_Trim      var     Byte 'trim value 128 = neutral trim, 0=-128, 256=128
JOY1Y_Trim      var     Byte 
JOY2X_Trim      var     Byte 
JOY2Y_Trim      var     Byte 
Temp_Trim       var     BYTE

JOY1X_GainH     con 6  'Gain for High end of stick 50-130% (5-13)
JOY1X_GainL     con 6  'Gain for Low end of stick 50-130% (5-13)
JOY1Y_GainH     con 6
JOY1Y_GainL     con 6
JOY2X_GainH     con 6
JOY2X_GainL     con 6
JOY2Y_GainH     con 6
JOY2Y_GainL     con 6
P1_GainH        con 10
P1_GainL        con 10

JOY1X_Max       con 1400  'pan
JOY1X_Min       con 800   'pan
JOY1Y_Max       con 1400  'tilt
JOY1Y_Min       con 800   'tilt 
JOY2X_Max       con 1400 
JOY2X_Min       con 800
JOY2Y_Max       con 1400
JOY2Y_Min       con 800
P1_Max          con 1850  'Aux Tilt
P1_Min          con 450   'Aux Tilt

Pulse_Start     con     400 '400us - fudge: Pulse Start (high) + chan pulse (low) = Total chan pulse
chan_adj        con     9 'fudge factor for pulses (used a scope to come up with value)
Chan_Ctr        con     1100
Chan1           var     word 'Aile
Chan2           var     word 'Elev
Chan3           var     word 'Thro
Chan4           var     word 'Rudd
Chan5           var     word 'Gear
Chan6           var     word 'Aux1
Chan7           var     word 'Aux2
Chan8           var     word 'Aux3
Chan1f          var     word 'Aile
Chan2f          var     word 'Elev
Chan3f          var     word 'Thro
Chan4f          var     word 'Rudd
Chan5f          var     word 'Gear
Chan6f          var     word 'Aux1
Chan7f          var     word 'Aux2
Chan8f          var     word 'Aux3

'Reverse Bits, Channel , Mode 1 (0=Normal, 1=Reverse)
Chan1_1R        con     0 'Drive Turn 
Chan2_1R        con     1 'Drive Speed
Chan3_1R        con     0 'Camera Tilt
Chan4_1R        con     0 'Camera Pan
Chan5_1R        con     1 'Aux Camera Tilt

'LCD Constants
LCD_CLR         con 88 'clear
LCD_INSTR       CON 254 'instruction command
LCD_L           con 71 'move curser to position 71 [column] [row]
LCD_H           CON 72 'move curser home
LCD_BL1         con 66 'backlight on, follow by minutes
LCD_BL0         con 70 'backlight off

ASM
INT_LIST  macro    ; IntSource, Label, Type, ResetFlag?
        INT_Handler TMR1_INT, _RC_Pulse, PBP, yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM

T1CON = %00000001           ; Prescaler = 1:1, TMR1ON
TMR1L = PreLoad.LowByte
TMR1H = PreLoad.HighByte    ; preload to give 22mS interrupts (at 1:1)

' /////////////////////////////////////////////////////////////////////////////
' Begin
' /////////////////////////////////////////////////////////////////////////////

high l1: pause 50: high l2: pause 50: high l3: pause 50: high l4: pause 50: high l5: pause 50 
low l1: pause 50: low l2: pause 50: low l3: pause 50: low l4: pause 50: low l5: low 50

'trim values retreived from eeprom
gosub Sub_Read_EEprom

if JOY1X_Trim = 255 and JOY1Y_Trim = 255 then   'means things are zeroed out (reprogrammed), so set defaults
    High L5: pause 250: low L5
    JOY1X_Trim = 128 
    JOY1Y_Trim = 128 
    JOY2X_Trim = 128 
    JOY2Y_Trim = 128 
    gosub Sub_Write_EEprom
endif

@ INT_ENABLE  TMR1_INT     ; enable Timer 1 interrupts

' /////////////////////////////////////////////////////////////////////////////
' Main Loop
' /////////////////////////////////////////////////////////////////////////////
mainloop: ' Main program loop

[mackrackit]

PORTA = %00000000 ' output logic at power-up
PORTB = %00000000 ' output logic at power-up
PORTC = %00000000 ' output logic at power-up
PORTD = %00000000 ' output logic at power-up
PORTE = %00000000 ' output logic at power-up
Try setting the TRIS registers here
TRISA = xxx
TRISB = xxx
_ _ _ _ _ _