' PIC_IO_BAS.bas PIC serial IO interface by Mark Phythian
' Uses Microchip PIC16F88 processor running at 4MHz internal RC Osc.

' define variables
Dim adtable(4) As Word  ' table to hold adc results
Dim chan As Byte        ' channel number
Dim val As Word         ' word size adc result variable
Dim oldb As Byte        ' last portb value
Dim char As Byte        ' single character commend
Dim command As Byte     ' upper 4 bits of command
Dim n As Byte           ' lower 4 bits of command
Dim m As Byte           ' byte size temporary variable
Dim wrd As Word         ' word size temporary variable

' setup PIC
OSCCON = 0x72           ' set internal RC select to 8MHz
TRISB = %11000000       ' set PORTB 0-5 pins as outputs, 6 & 7 inputs
Gosub initad            ' initialise adc
PIE1.RCIE = 1           ' enable UART RX interrupt
OPTION_REG = 0x7f       ' enable PORTB weak pullups for inputs 6 & 7
Hseropen 57600          ' set UART BAUD rate
INTCON = 0xc8           ' enable GIE, PEIE and RBIE

' initialise variables
PORTB = 0x00
oldb = PORTB And 0xc0   ' last value of PORTB bits 6 & 7 for change of state
WaitMs 1000
Hserout "OK"            ' startup ok
WaitMs 100

' endless loop converting as fast as possible
main:

While 1
  ADCON0 = 0xc1	        ' select channel 0 in bits 5,4,3 of ADCON0

  For chan = 0 To 3
    Gosub adconv        ' go to conversion routine
    val.HB = ADRESH     ' save high byte (upper 2 bits only)
    val.LB = ADRESL     ' save low byte
    adtable(chan) = val
    ADCON0 = ADCON0 + 0x08  ' increment selected channel
  Next chan
Wend  'repeat forever
End

' Initialise ADC
initad:
TRISA = %11111111	' set portA as input
ANSEL = %00001111       ' set PORTA pins 0-3 as analog inputs
ADCON1 = 0x80           ' set 10 bit A/D result format right justify ADRESH/L
ADCON0 = 0xc1           ' set A/D conversion clock to internal source, turn on adc
Return

' Adc conversion routine
adconv:
High ADCON0.GO_DONE     ' start the conversion
While ADCON0.GO_DONE    ' wait until conversion is completed
Wend
Return

On Interrupt
Save System
' check for PORTB change of state on bits 6 & 7
If INTCON.RBIF = 1 Then  ' test if portb change flag is on
  n = PORTB And 0xc0
  INTCON.RBIF = 0       ' reset RBI flag
  n = oldb Xor n
  If n.7 = 1 Then	' if bit 7 changed
    If oldb.7 = 1 Then  ' if bit 7 changed to 0
      Hserout 0x22      ' send a " for INT2 input trigger
      WaitMs 10
    Endif
  Else
    If n.6 = 1 Then     ' if bit 6 changed
      If oldb.6 = 1 Then  ' if bit 6 7 changed to 0
	Hserout 0x21    ' send a ! for INT1 input trigger
	WaitMs 10
      Endif
    Endif
  Endif
  oldb = PORTB And 0xc0  ' set oldb to new PORTB value
Else

' test for serial command received
  If PIR1.RCIF = 1 Then  ' test if RXer flag is on
    PIR1.RCIF = 0        ' reset RCI flag
    Hserget char         ' get the received character
    command = char And 0xf0  ' command is upper 4 bits
    n = char And 0x0f    ' number is lower 4 bits

' fetch 10 bit adc values, returns 2 bytes each, command letter 0 (zero)
    If command = 0x30 Then
      Hserout char       ' echo command
      WaitMs 10
      For n = 0 To 3
        Hserout adtable(n) ' send 10 bit value in 2 bytes
        WaitMs 10
      Next n
    Else

' fetch 8 bit adc values, returns 1 byte each, command letter @
      If command = 0x40 Then
        Hserout char       ' echo command
        WaitMs 10
        For n = 0 To 3     ' D command requests all 4
	  wrd = adtable(n)
	  m = ShiftRight(wrd, 2)
	  Hserout m        ' send 8 bit value as 1 byte
	  WaitMs 10
        Next n
      Else

' read inputs bits PA4-7, returns 1 byte, command letter P
        If command = 0x50 Then
          Hserout char     ' echo command
          WaitMs 10
          n = PORTA And 0xf0
          n = ShiftRight(n, 4)
          Hserout n        ' send 4 bits in low part of byte
          WaitMs 10
        Else

' set outputs, command letters (from $60-$6F) ',a,b,c,d ... o
          If command = 0x60 Then
            Hserout char  ' echo command
            WaitMs 10
            m = n And 0x03  ' arrange bits to Port B bits 4,3,1,0
            n = n And 0x0c
            n = ShiftLeft(n, 1)
            PORTB = m Or n  ' set output bits from number n
          Endif
        Endif
      Endif
    Endif
  Endif
Endif
exit:
Resume