Using PPS when PPSTool unavailable.

[mkstevo]

As I've written before, I use a Mac for my GCB programming. At the moment the PPS Tool isn't available for the Mac. I recently ordered some PIC16F18877 processors for work as part of a potentially large project and today decided to have a look at them, and try and start to use them. A simple program I'd written for the 16F1825 which used interrupts, a serial LCD module and the millis() function by Chris Roper was loaded into my editor and compiled.

Millis() returned an error message that TMR0 did not work correctly with this processor as Chris has stated, so all references to millis() were removed, and the program re-compiled.
Success!
Well, no!
Although the program compiled perfectly well now, nothing appeared to work. The serial LCD refused to display anything and the button and buzzer did nothing either. Hmm. Why?

I looked at the datasheet and could see that the Serial TX function is assigned by PPS. As the Mac can't use the PPS tool, I fired up a VirtualPC and installed the PC build of GCB onto it and ran the PPS tool which gave me this:

    'Generated by PIC PPS Tool for Great Cow Basic
    'PPS Tool version: 0.0.5.25
    'PinManager data: v1.75
    'Generated for 16f18877
    '
    'Template comment at the start of the config file
    '
    #startup InitPPS, 85
    #define PPSToolPart 16f18877

    Sub InitPPS
        UNLOCKPPS

            'Module: EUSART
            RC6PPS = 0x0010    'TX > RC6

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

Adding that into my code gave me a working Serial LCD. {Well it did once I counted the pins correctly and plugged the serial connection into the right pin...}

Next to look at the Interrupt.

Again the datasheet suggested this could be adjusted using PPS, so I went back to the VirtualPC and the PPS tool gave me this:

    'Generated by PIC PPS Tool for Great Cow Basic
    'PPS Tool version: 0.0.5.25
    'PinManager data: v1.75
    'Generated for 16f18877
    '
    'Template comment at the start of the config file
    '
    #startup InitPPS, 85
    #define PPSToolPart 16f18877

    Sub InitPPS
        UNLOCKPPS

            'Module: EUSART
            RC6PPS = 0x0010    'TX > RC6
            'Module: EXT_INT
            INTPPS = 0x0002    'RA2 > INT

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

Now my interrupt worked too, along with the buzzer.

Looking at the generated PPS code I wondered how I could 'decode' the datasheet, into PPS code without needing to use the PPS tool I don't have easy access to.

For the 16F18877 the relevant pages in the manual are 241, 243 and 246. Page 241 lists the names of the input PPS funtions, page 243 lists the pin 'values' that need to be assigned to the function. For the external interrupt, the constant given on page 241 is INTPPS. The value for PortA.2 is given on page 243 as 0x02. In order to set the PPS for an external interrupt on PortA.2 the required code would be:

INTPPS = 0x02

Just as given by the PPS tool.

Moving on to the Serial TX, page 246 tells us that the output pins for PPS are set using the command:
RxyPPS where the 'xy' is replaced by the pin notation of the required pin. So for pin PortC.6 this gives the command of: RC6PPS ('xy' being replaced by 'C6'). The instruction value for Serial TX is shown as 0x10 making the the code for Serial TX on PortC.6:

RC6PPS = 0x10

Again, just as produced by the PPS tool.

Editing my code to read:

'Uses 16F18877, Serial LCD, PPS function mapping and interrupts for a button.

'The interrupt triggers on a rising then falling edge to enable 
'counting of buttons only when a button is pressed and released.

'The button state is stored at startup to allow for buttons that
'may idle high or low automatically.

#Chip 16F18877, 32
#Option explicit
#Config CP=On

#Include "Simple_Serial_LCD.h"
'Simple_Serial_LCD.h provides a simple interface to an
'attached serial LCD display. The ports used for the
'serial interface should be defined in program code
'for portability.

 #startup InitPPS, 85 
 'Set a startup routine with a high priority of 85.
 'Comms routines have a priority of 90, so setting this below that 
 'ensures PPS is set before any comms routine is attempted.
 '80 is the highest priority, 100 is 'normal' priority.
 #define PPSToolPart 16f18877

 Sub InitPPS
    UnlockPPS       'Unlock PPS to allow changes
    RC6PPS = 0x10   'Assign PortC.6 to Serial TX

    INTPPS = 0x02   'Assign External Interrupt to PortA.2
    LockPPS         'Lock PPS to prevent changes
End Sub

'*******************************************************************
'*******************************************************************
'*******************************************************************


' Define the USART port
#Define USART_BAUD_RATE 9600
#Define USART_BLOCKING
#Define SerOutPort portC.6 'Pin  25
#Define Button     PortA.2 'Pin  4
#Define Beeper     PortC.3 'Pin  18  'This connects directly to a 12V Piezo buzzer
                                     'the fact that a 12V buzzer is driven from a 5V pin
                                     'does not matter. It is loud enough to hear!

Dim         TimeCount       As Long
Dim         BeepCount       As Byte
Dim         Pressed         As Bit


Dim         Reset_Trigger   As Bit
Dim         Trigger         As Bit


'Set pin directions
Dir SerOutPort  Out         'Pin  25
Dir Beeper      Out         'Pin  18
Dir Button      In          'Pin  4

Let Reset_Trigger = 0
Let Trigger       = 0
Let TimeCount         = 0

Initialise
Test

Sub Test


    Do

        SerLocate(0,0)
        HSerPrint TimeCount

        If Trigger = 1 Then
            SerLocate(1,0)
            HSerPrint TimeCount
            HSerPrint "                "
            Let Trigger = 0
            DoBip(1,25)
        End If

        If Reset_Trigger = 1 Then
            SerLocate(1,11)
            HSerPrint TimeCount
            HSerPrint"    "
            Let Reset_Trigger = 0
            DoBip(1,25)
        End If

        TimeCount++

    Loop

End Sub

Sub Initialise

    Do
        If Button = Pressed Then
            Let Pressed = !Button
            Let TimeCount = 0
        End If
        Wait 5 mS
        TimeCount++
    Loop Until TimeCount > 125 'Get the idle state of the button pin
    Let TimeCount = 0

'For the serial LCD to initialise, there must be a few
'milliseconds of delay before using the serial LCD.
'This is provided by the button test above.
'Otherwise, add some delay here.

    ClearScreen
    SerLocate(0,0)
    HSerPrint " Hello 16F18877 "
    SerLocate(1,0)
    HSerPrint "& Fast Interrupt"

    '**********************************************************************
    'Interrupt setup
    '**********************************************************************

    'Option_Reg for rising/falling edge
    'INTEDG

    'INTEDG = 1 'Rising Edge
    'INTEDG = 0 'Falling Edge

    Let INTEDG = Pressed      'Interrupt on switch pressed state

    'INTE = 1 'Interrupt on Edge enabled
    'INTE = 0 'Interrupt on Edge disabled

    'INTF = 1 'Edge Interrupt happened
    'INTF = 0 'No Edge Interrupt

    'INTE = 1 'Interrupt on Edge enabled
    'INTE = 0 'Interrupt on Edge disabled

    Let INTE   = 1 'Interrupt on Edge enabled
    Let INTF   = 0 'Clear any interrupts

    On Interrupt ExtInt0 Call Interrupt_Sub
    '**********************************************************************
    'Interrupt setup
    '**********************************************************************
    Wait 250 mS
    ClearScreen

End Sub

Sub Interrupt_Sub

    If INTF = 1 Then
        If Button = Pressed Then             'Button pressed
            Wait 10 mS
            If Button = Pressed Then         'Still pressed
                Let Trigger  = 1
                Let INTEDG = !Pressed
            End If
        End If
        If Button <> Pressed Then             'Button released
            Wait 10 mS
            If Button <> Pressed Then         'Still released
                Let Reset_Trigger = 1
                Let INTEDG = Pressed
            End If
        End If
        'Let INTF   = 0 'Clear interrupt
    End If

End Sub

Sub DoBip(In NumberOfBips As Byte, LengthOfBips As Word)
    For BeepCount = 1 To NumberOfBips
        SoundBeep(1) 'Beep on
        Wait LengthOfBips mS
        SoundBeep(0) 'Beep off
        Wait LengthOfBips mS
    Next
End Sub

Sub SoundBeep(In Sound As Bit)
    Let Beeper = Sound
    'Turn on or off the beeper
End Sub

Gave me fully working code.

I don't imagine this comes close to describing the complexities of the PPS function assignments, in almost all cases I would recommend that if you have access to the PPS tool, that it is used, if you don't however, this may give some insight into how to generate working code for setting those functions.

In my case the '#Define PPSToolPart 16F18877' assignment seemed not to be required, as I was unsure of it's significance, I left it in for the sake of completeness. The PPS tool sets a StartUp Function to set the PPS assignments as soon as the processor starts. I copied this method to ensure the PPS functions are set before anything else executes.

The datasheet implies (if I read it correctly) that the Serial TX function defaults to PortC.6 during power on reset. For me, this didn't seem to be the case. Perhaps I didn't read that bit correctly?

[Chris Roper]

Hi mkstevo ,

I have a new version of millis that should support your part.
I have not released it yet as I am still testing and documenting but I attach it here for you to try.

Cheers
Chris

[mkstevo]

I have just tested that using the 'new' millis(), and it does work just as it did on the 16F1825. Many thanks for the updated version.