HPWM help/problem

[Paul Haug]

I am trying to use HPWM for modulating a proportional hydraulic valve to replace an existing circuit that no longer functions correctly.
I am using a 18F26K20 and I am using a code sample from the basic manual. (code sample was a 16F877A, 20)
I need to get the pulse repetition rate down to 50 Hz.
With the clocks set at 16 MHz I get the proper proportional rate at 1 kHz when I set the HPWM rate to 1
I have tried reducing the clock rate to different values but non work that make any sense below 32 MHz and 16 MHz.
Any suggestions would be of great value.
Here are the rep rates for various #chip 18F26K20 , x
x= 32 rep rate is 2Khz
x=16 rep rate is 1 kHz
x=8 rep rate jumps up to 2 kHz ????
x= 10 rep rate is 100 hz (probably an illegal setting for this chip?

'This will be the pwm modulator for porportional hydrolic valves
'PEH Oct 29 2017
'ASM Ver 0.97.01
'This program will alter the brightness of an LED using
'hardware PWM.
'Select chip model and speed

#Option Explicit
#chip 18F26K20 , 16  ;10 make slow clk, but 10 doesn't make sense ???
#config Osc = int
#config mclr=on            ;reset PB enabled

'Set the CCP1 pin to output mode
DIR PORTC.2 out
Dim Bright as byte ;

'Main code
do
'Turn up brightness over 2.5 seconds
For Bright = 1 to 255
HPWM 1, 1, Bright
wait 10 ms
next
'Turn down brightness over 2.5 seconds
For Bright = 255 to 1
HPWM 1, 1, Bright
wait 10 ms
next
loop

[Anobium]

@Paul. Can share your version of the compiler? I think you are on v09.01. You need to be on v.0.98

Update your setup as i have updated. PMW and I will be using the latest build here to help you.

[Anobium]

Based on using v0.98.0x (I have v0.98.01 here... I will release this week).

1. The operating frequencies for the internal clock are 64, 32, 16, 8, 4, 2, 1, 0.5, 0.25. So, 10 would need an external oscillator.
2. This chip has a specific configuration for the the oscillator. Internally, with GCBASIC we call this 'IntOSCCONFormat'. So, you need v0.98.xx to support the clock correctly.
3. I have just tested you code and it works a treat here using the v.98.xx

Upgrade your installation please.

Is your question... what are the PWM frequencies (a range) supported at each chip frequency?

[Anobium]

And, if you want to check that a PWM frequency is supported by a chip frequency when using CCP/PWM.

Try the fixed mode first. This will issue an error message if the PWM frequency is NOT supported by a chip frequency.

#chip <whateventchip>, <whatever chip frequency >
#define PWM_Freq 1      'Frequency of PWM in KHz
#define PWM_Duty 50      'Duty cycle of PWM (%)
HPWMOn 1

Also, in the latest build you can test...

'Add this to your user program.
'A test piece of to test whether your desired Frequency for chip frequency and PWM frequency.
'Why ? If you chip has not got bit T2CKPS2 then maximum Timer2 Clock Prescale is 16, so, we can test if we have overflowed.  The post scaler is 1 - so, we are limited to a specific range of freqencies.

#ifndef bit(T2CKPS2)    'This tells us the the Timer2 Clock Prescale is limited to 16

  'USART settings - setup the serial port - connects to default port
  #define USART_BAUD_RATE 9600
  #define USART_TX_BLOCKING

  HSerPrintCRLF 2
  'If bits 0 and 1 of T2CON are set then we HAVE overflowed!!
  '00 = Prescaler is 1
  '01 = Prescaler is 4
  '1x = Prescaler is 16
  '11 = Overflowed!  We use the two bits to show we have an overflow condition
  if t2con and 3 = 3 then
      HSerPrint "Error - Lower Chip Frequency, "
      HSerPrint "or raise PMW Frequency!"
      HSerPrintCRLF
  else
      HSerPrint "Chip and PWM Frequency OK!"
  end if
#endif

:-)

[Paul Haug]

I have upgraded to V0.98.00 as you suggested, but any thing below clock selection (internal) of 16 or 32 mhz gives strange results on the HPWM repition rate.
Your question of:
Is your question... what are the PWM frequencies (a range) supported at each chip frequency?
That is my problem, I need 50Hz (or approximatly) for the hydro valves to operate correctly.
.
I will try your suggestions today with the HserPrint as a debug test.
Thanks

[kent_twt4]

Typically you would need 14-16bit PWM or CCP for 50Hz refresh rates, at least with a reasonable clock source.

Here William uses a TMR1 (16bit) interrupt and "Wait cycles" to update 4 servos https://sourceforge.net/p/gcbasic/discussion/629990/thread/8e7f88d7/#0ce3

Here is tutorial on using an AVR for 50Hz PWM updates (non blocking) https://sourceforge.net/p/gcbasic/discussion/projects%26guides/thread/66153766/#ae47

[Paul Haug]

Thanks kent_twt4,
That certianly gives me another approach since my application is closely related to RC servo control, except I need full (0-100%) pulse width control, but with some tweeking that code should work.

[Anobium]

And... look in your installation.

..Demos\Interrupt_and_Timer_Solutions\Interrupt - Timed examples

There is a set of calculators - this WILL show the range of frequencies per a selected chip freq. See the TimerCalculator for the calculator for 50 hz... it is a max chip freq of 8mhz on your chip.

//Timer2
//Prescaler 1:16; Postscaler 1:10; TMR2 Preload = 250; Actual Interrupt Time : 20.005 ms

:-)

[kent_twt4]

The 18f26k20 has a TMR3 to play with too, so you could sync up a full scale PWM duty cycle using a TMR3 count (or overflow) + interrupt, in the TMR1 interrupt.

As Evan shows, plenty of ways to get what you need. Using the CCP special event trigger is another option.

[William Roth]

@Paul

Aparantly neither Microchip nor GCB figured that anyone would want/need to use Hardware PWM at less than 1Khz.

The 18F26K20 only allows for one possible clock source for TMR2 and that is FOSC/4. So we are stuck with that. Using the internal osc (chip MHz) we can get to 50 hz PWM only one way. That is by setting the Chip MHz to 2 and then manually setting the Timer2 Prescale to 128 and the Timer2 Period Register ( PR2) to 152

The problem with this is that changing the duty cycle on-the-fly using HPWM function will likely be glitchy as it will reset the timer period to an unwanted value. You may be able to write the CCPR1H duty register directly, bypassing the high level GCB HPWM command which always reset the timer period.

My suggestion for 50Hz PWM with GCB on your chip is to bit bang it usiing a 16 bit timer. Optionally you could get a more modern chip that supports multple clock sources to TIMER2//4/6 and that has Dedicated PWM modues.

50 Hz is a common frequency for Servo contol. If you are wanting to control a servo then please indicate so as 8- bit PWM will not give the resolution necessary for good Servo control.

Below is Example Code (Untested) that should show to get 50 hz PWM using a 18F26K20 with 2Mhz Internal Clock Source . I created a sub to set duty cycle as a percentage to eliminate to need to use HPWM to change duty cycle. Use this only if you can live with a 2 Mhz system cock.

#chip 18Ff26k20, 2
;// Add Config options as necessary

#option Explicit

Dir PORTC.1 OUT       ; >>>> PWM
HPWM (1, 1, 20)       ; start PWM
PR2 = 153             ; override GCB Setting
T2CON = b'11100000'   ; Pre = 1:128 /Override  HPWM Settings

DIM DutyVal as Byte

Do
    For DutyVal = 0 to 100
          SetDuty (DutyVal)    ;In percentage
          Wait 100 ms
    Next

    For DutyVal = 100 to 0 Step -1
        SetDuty (DutyVal)    ;In percentage
        Wait 100 ms
    Next

 Loop

Sub SetDuty (in TMPVar1 as Byte )
     '// Sets duty from 0 to 100 percent
     CCPR1H = ([WORD]TMPVAR1 * 154) / 100
End Sub

[stan cartwright]

50Hz pwm would have to lower chip clock speed to get pwm resolution I found.
for a servo why not interrupt pulseout..my idea of servo is model controller actuator not servo motor.
~~~
;set up servo interrupt 50Hz
on interrupt timer1overflow Call servo
inittimer1(OSC,PS1_2)
Starttimer 1
;
sub servo ;servo interrupt
settimer 1, 25535
pulseout Servo_Pin , servoposition 10us
end sub
~~~

[Paul Haug]

Many thanks, I will work on the various suggestions.
This is for a rather large hydraulic control system that uses proportional valves that look like solenoids. By scoping the working units I see the pulses are at 50Hz and duty cyle of the pulses is 0 to 100%, zero being closed and 100% being fully opened.
* 8 bit resolution will be fine, the operator uses a joy stick to control the speed of lift, drive, swing of a platform. Many safety switches and limits are used that the uProc will not control.
The software will be doing other things also, like logging temp, operating relays and indicator lights and a serial output.
EDIT: Added some comment info.

[William Roth]

@Paul

The 18F26K20 has 64K Flash and 4K SRAM. So I assume this chip was not just randomly selected, but was slelected for its large amount of memory an/or its 64MHz max speed

A newer alternative is the 18F26K40. This chip has the same memory & speed specifications but includes a wealth of new features and new perieherals.

In regards to your applcation the 18F26K40 has updated Timer2/4/6 modules that support multiple clock sources, and it also has a Reference Clock Module. This makes it relatively easy to get a 50 Hz PWM while operating the chip at up to 64Mhz.

The idea is to clock Timer 2 using the Reference Clock, then to use Timer2 as the clock source for the CCP or PWM module used for the PWM.

While GCB's PWM library does not yet support all the possible clock source combinations for HPWM, with a few extra lines of code a 50Hz is quite possible.

And the newer/better chips are less expensive.

Cost Comparison (Mouser):
18F26K20 ... $3.02
18F26K40 ... $2.04
18F27K40 ... $2.34

Below is working example code using a PIC18F27K40 that I had laying around, the only difference being is that the 18F27K40 has 128K Flash instead of 64K with the 18F26K40. Hook your scope up to PIN C.1 to see the output. Or attach an LED.

; Unofficial Example/Demo of Low Frequency (50Hz) PWM
; Uses CCP1/Timer2 & Reference Clock Modules
; William Roth

'Chip Settings.
#chip 18f27k40, 32
#config FEXTOSC = OFF, RSTOSC = HFINTOSC_64MHZ, LVP = ON
#option Explicit
#startup InitPPS, 85

' Define I2C settings
#define HI2C_BAUD_RATE 125
#define HI2C_DATA  PORTC.4
#define HI2C_CLOCK PORTC.3  ;unnecessary

'Initialise I2C
Dir HI2C_DATA IN
Dir HI2C_CLOCK IN
HI2CMode Master

'''Set up LCD
#define LCD_IO 10
#define LCD_I2C_Address_1 0x7E
#define LCD_SPEED Fast
#define LCD_Backlight_On_State  1
#define LCD_Backlight_Off_State 0
CLS
InitLCD  'Just in case but probably unnecessary

DIM DutyVal as Byte    ' set aside variable for duty cycle
Dir PORTC.1 OUT         ; PWM out on Pin C.1 (see InitPPS Sub)

HPWM (1, 1, 0)          ; Start CCP1 PWM with zero Duty (off)

 'These lines override settings of HPWM library and allow 50 hz PWM
PR2 = 156               ; Override HPWM Setting of period register
CLKRCON = 0b10010110    ; Config & start Reference Clock Module
T2CLKCON = 0b00000111   ; Set timer2 Clk source as Reference Clock Out
T2CON = 0b11100000      ; Override  HPWM Setting of T2 Prescale

 '// Splash scren
CLS : Wait 1 S
Call SPLASH

'// Test PWM from 0 to 100 percent duty
Do
    For DutyVal = 0 to 100
        SetDuty (DutyVal)    ;In percentage
        Wait 20 ms
    Next

    'Wait 2 s

    For DutyVal = 100 to 0 Step -1
        SetDuty (DutyVal)    ;In percentage
        Wait 20 ms
    Next

    'Wait 2 S
Loop

Sub SetDuty (in TMPVar1 as Byte )
    CCPR1L = 0
    CCPR1H = ([WORD]TMPVAR1 * 157) / 100
End Sub

SUB SPLASH
    CLS
    Print "Great Cow BASIC"
    Locate 1,0
    Print "Ver 0.98.01"
END SUB

Sub InitPPS
    'Module: CCP1
    RC1PPS = 0x0005    'CCP1 > RC1
    CCP1PPS = 0x0011    'RC1 > CCP1 (bi-directional)

    'Module: MSSP1
    RC3PPS = 0x000F    'SCL1 > RC3
    SSP1CLKPPS = 0x0013    'RC3 > SCL1 (bi-directional)
    RC4PPS = 0x0010    'SDA1 > RC4
    SSP1DATPPS = 0x0014    'RC4 > SDA1 (bi-directional)
End Sub

[Paul Haug]

Many thanks William. I used the 18F26K20 because I had a tube full left over from a now defunct project.
I will order some 18F27K40 and try out your code as it looks simple and straight forward.
It may be just what I need.

[Paul Haug]

On the 18F27K40 with the 28 pin package it doesn't show a transmit pin for EUART, it shows a receiver pin for UART, so I guess I need to order the 40 pin package, which is a little clumsy for my PC board that I have laid out for general-purpose 28 pin usage
I looking at the allocation table in microchip for this part and it doesn't show EUART TX. For the 28 pin package
Am my correct or am I misreading microchip pin allocation table.
I really need the serial output capability.

[Chris Roper]

The 18F27K40 uses PPS (Peripheral Pin Select) and you can use it to
assign TX to, within reason, any pin of your choice.
Look up PPS in help and also in the Datasheet.
PPS can be confusing at first but a fantastic facility once you grasp its
capabilities.

On 31 October 2017 at 22:30, Paul Haug binary1248@users.sf.net wrote:

On the 18F27K40 with the 28 pin package it doesn't show a transmit pin for
EUART, it shows a receiver pin for you start, so I guess I need to order
the 40 pin package, which is a little clumsy for my PC board that I have
laid out or general-purpose 28 pin usage
I looking at the allocation table in microchip for this part and it
doesn't show EUART TX. For the 28 pin package
Am my correct or am I misreading microchip pin allocation table.
I really need the serial output capability.

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HPWM help/problem
https://sourceforge.net/p/gcbasic/discussion/579126/thread/5ac86912/?limit=25#c93e

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[William Roth]

Sorry, but you are incorrect.

This chip supports PPS (Peripherial Pin Select) . This basically means you you can assign any Pin on PortB or PortC to be TX (or RX for that matter). TX is simply not assigned by default. This add lots of flexibility.

To assign TX out to a specific Pin, open the PPS tool and enter the specific chip at the top. Then in "Peripheral Output" Select TX1 and assign the pin you want. Let's use RC6 which is the same as most older 28 Pin chips. Then click "Add"

I like to also assign RX even if it is the default so in "Peripheral Input" Slelect RX1 and make it RC7. Then click on "Add". Code will be generated in the output window that you can then copy/paste into your GCB program. It will look something like this:

   'Generated by PIC PPS Tool for Great Cow Basic
'PPS Tool version: 0.0.5.11
'PinManager data: v1.55
'
'Template comment at the start of the config file
'
#startup InitPPS, 85

Sub InitPPS

        'Module: EUSART1
        RX1PPS = 0x0017    'RC7 > RX1
        RC6PPS = 0x0009    'TX1 > RC6
        TX1PPS = 0x0016    'RC6 > TX1 (bi-directional)

End Sub
'Template comment at the end of the config file

You then need to setup serial in GCB same as before.

The Subroutine "InitPPS" runs at the very beginning of the program, so any peripherial that needs pins assigned should be added here as pins must be assigned before the respective libraries initialize the peripheral devices.

Note that in the code I previously posted that Pins were assigned for the MSSP (I2C) and for CPP1 (PWM)

Pretty cool stuff.

Edit: Corrected my mistake in assigning RX1 to RC5 instead of RC7

[Paul Haug]

WOW, thanks all, is there any thing this chip can't do. The PPS is really cool, but I need to study it and learn it's flexability. William that is a great example.

[Paul Haug]

I have ordered 18F27K40 chips to use and explore some of it's many options.
Thanks William.

[William Roth]

Great Paul,

Please do me a favor. When they arrive can you tell me what silicon revision you receive and where you ordered them from. I have revison a002.

[stan cartwright]

I googled 18F27K40 and nothing..?

[Chris Roper]

I googled 18F27K40 and nothing..?

That is wierd when I google it this is the first result:
http://www.microchip.com/wwwproducts/en/PIC18F27K40

[William Roth]

When using google to search for a PIC chip, I find that the search results are better when "PIC" is included with the model number. e.g. "PIC18F27K40"

[stan cartwright]

True. Looks capable from glimpse. guess it needs pk3 to program features if it's got programable pins.
Thanks.

[Paul Haug]

William,
Yes I will let you know the version niumbers and I ordered from mouser.
Looking at your code I see you are using I2C for debug display so I have a few questions:
;
1) Type or model of LCD unit. I have been using a rs232 type unit, but like to use I2C to learn more about I2C type comm.
2) In your code (see section of code) you show I2C DIR data and clock as inputs but I don't see outputs ??

' Define I2C settings
#define HI2C_BAUD_RATE 125
#define HI2C_DATA PORTC.4
#define HI2C_CLOCK PORTC.3 ;unnecessary

            'Initialise I2C
                Dir HI2C_DATA IN  ;IN ???? where is out
                Dir HI2C_CLOCK IN ;IN ????  "    "   "
                HI2CMode Master

    '''Set up LCD
                    #define LCD_IO 10
                    #define LCD_I2C_Address_1 0x7E
                    #define LCD_SPEED Fast
                    #define LCD_Backlight_On_State  1
                        #define LCD_Backlight_Off_State 0
    CLS
    InitLCD  'Just in case but probably unnecessary