Working with an Optical Rotary Encoder

'************************************************* ************************************************
'* Bournes Optical Encoder with PIC® 18F452 or possibly ANY 18F PIC®. *
'* Uses Hardware Interrupt on PortB.1 with a Bournes 256 Cycle per rev encoder *
'* Joe Hanley (Captainslarty at yahoo.co.uk) *
'* Feb 2009 *
'* WE ARE USING PORTB.1 for the interupt, and PORTB.3 for the other signal *
'* THIS FREES UP THE OTHER INTERRUPT PINS FOR OTHER USES.. *
'************************************************* ************************************************


Device 18F452
XTAL 20

Include "proton18_g20joe.int" ' GLCD Routines only... add your own here.

' Here are our register symbols that include the Interrupts in use
' we are only using a limited few, but the COMPLETE register contents are listed for information
' If you are new to Interrupts, dont be put of by this huge list. !
' It could be written as just ....

'Symbol IPEN = RCON.7 ' Interrupt Priority Enable bit
'Symbol PEIE = INTCON.6 ' Peripheral Interrupt Enable
'Symbol GIE = INTCON.7 ' Global Interrupt Enable
'Symbol INT1IF = INTCON3.0 ' INT1 External Interrupt Flag 1 = The INT1 external interrupt occurred (must be cleared in software)
'Symbol INT1IE = INTCON3.3 ' INT1 External Interrupt Enable 1 = Enables the INT1 external interrupt PortB1
'Symbol INT1IP = INTCON3.6 ' INT1 External Interrupt Priority bit 1 = High priority PortB1

' and nothing more is needed - you could delete all the other symbol declares.

' But for a fuller explanations, here are the contents of all the register used, see the datasheet for your device.

Symbol NOT_BOR = RCON.0 ' Brown-out Reset Status bit
Symbol NOT_POR = RCON.1 ' Power-on Reset Status bit
Symbol NOT_PD = RCON.2 ' Power-down Detection Flag bit
Symbol NOT_TO = RCON.3 ' Watchdog Time-out Flag bit
Symbol RI = RCON.4 ' RESET Instruction Flag bit
Symbol IPEN = RCON.7 ' Interrupt Priority Enable bit
'1 = Enable priority levels on interrupts

Symbol RBIF = INTCON.0 ' RB Port Interrupt Flag
Symbol INT0IF = INTCON.1 ' INT0 External Interrupt Flag
'1 = The INT0 external interrupt occurred (must be cleared in software) PortB0 ALways HIGH
'0 = The INT0 external interrupt did not occur PortB0
Symbol TMR0IF = INTCON.2 ' TMR0 Overflow Interrupt Flag
Symbol RBIE = INTCON.3 ' RB Port Change Interrupt Enable
Symbol INT0IE = INTCON.4 ' INT0 External Interrupt Enable
'1 = Enables the INT0 external interrupt PortB0 Alwyas HIGH
'0 = Disables the INT0 external interrupt PortB0
Symbol T0IE = INTCON.5 ' TMR0 Overflow Interrupt Enable

Symbol PEIE = INTCON.6 ' Peripheral Interrupt Enable same as GIEL
Symbol GIEL = INTCON.6 ' Low priority peripheral interrupt
'When IPEN = 1:
'1 = Enables all low priority peripheral interrupts
'0 = Disables all low priority peripheral interrupts

Symbol GIEH = INTCON.7 ' Enable all high priority interrupts same as GIEH
Symbol GIE = INTCON.7 ' Global Interrupt Enable
'When IPEN = 1:
'1 = Enables all high priority interrupts
'0 = Disables all interrupts

Symbol RBIP = INTCON2.0 ' RB Port Change Interrupt Priority bit 1 high 0 low
Symbol INT3IP = INTCON2.1 ' unimplemented - read as 0
Symbol TMR0IP = INTCON2.2 ' TMR0 Overflow Interrupt Priority bit 1 High 0 Low
Symbol INTEDG3 = INTCON2.3 ' Unimplemented - read as 0
Symbol INTEDG2 = INTCON2.4 ' External Interrupt2 Edge Select bit PortB2 edge Rising If 1 falling if 0
Symbol INTEDG1 = INTCON2.5 ' External Interrupt1 Edge Select bit PortB1 edge Rising If 1 falling if 0
Symbol INTEDG0 = INTCON2.6 ' External Interrupt0 Edge Select bit PortB0 edge Rising if 1 falling if 0 Always High Priority
Symbol NOT_RBPU = INTCON2.7 ' PORTB Pull-up Enable bit - 1 disabled - 0 PORTB pull-ups are enabled by individual port latch values

Symbol INT1IF = INTCON3.0 ' INT1 External Interrupt Flag 1 = The INT1 external interrupt occurred (must be cleared in software)
Symbol INT2IF = INTCON3.1 ' INT2 External Interrupt Flag 1 = The INT2 external interrupt occurred (must be cleared in software)
Symbol INT3IF = INTCON3.2 ' unimplemented - Read As 0
Symbol INT1IE = INTCON3.3 ' INT1 External Interrupt Enable 1 = Enables the INT1 external interrupt PortB1
Symbol INT2IE = INTCON3.4 ' INT2 External Interrupt Enable 1 = Enables the INT2 external interrupt PortB2
Symbol INT3IE = INTCON3.5 ' unimplemented - Read As 0
Symbol INT1IP = INTCON3.6 ' INT1 External Interrupt Priority bit 1 = High priority PortB1
Symbol INT2IP = INTCON3.7 ' INT2 External Interrupt Priority bit 1 = High priority PortB2


' Interrupt on port b 0 to 2 - we will use portb.1
' use pin b1 (we can set priorities on B1 and B2 , portB0 is ALWAYS high priority.)
' to set up the interrupt... for PortB.1 high priority..

INT1IP = 1 ' High Priority interrupt on PortB.1
INTEDG1 = 1 ' rising edge on PortB.1

' enable the Interrupt 1
INT1IE = 1

' Flags for the interrupts are ...
INT1IF = 0 ' make sure its clear to start with.

'set up any variables

' If you use a Byte for the 2 items below, then the MAX count is 0 to 255, a word allows 0 to 65535
' with the conditioning in the Interrupt service routine you can limit the count to any vlaue within the range - see notes there.

Dim Count_Encoder As Word ' encoder counter - use byte word or anything to suit your purpose. !
Dim Encoder_Now As Word ' this is the interim storage for the value from the interrupt, must be same type as above

' We have hardware Interrupts

ON_INTERRUPT GoTo ISR ' hardware interrupt

' Jump over the Interrupt Service Routine

GoTo Over_Interrupt

'Interrupt Routine

ISR: ' Interrupt Service Routine

Context SAVE ' we are using an 18 series. SOMETIMES you do not HAVE
' to use this command with 18, check the datasheet
' Here yo DO, not using it will cause GLCD corruption at high rotation speed

' check PortB1 INT1IF, if = 1 then THIS was the interrupt

If INT1IF<>1 Then Get_Out ' it wasn't us ! so clear off
If PORTB.3=1 Then Count_Up ' if the other pin is 1 then up, otherwise down....
Dec Count_Encoder

' Here is some conditioning for the total value of the counter.
' lets say we want a maximum reading of 1024.... a Word is 0 to 65535
' so when re reach 65535 we have clocked down from 0, so reset to your desired max count
' this will act like a tuning knob, clocking over when the count is reached.
' in other circumstance you may want to use the encoder like a volume control
' where a stop is reached, so if its 0 and you continue turning anticlcokwise it stays at 0
' and when the count is reached, and you continue turning clockwise, it remains at that count.
' here it is set as an example for the volume control type with a range of 0 to 1024
' un rem the other lines to try the clockover type, and rem out the volume lines.

'If Count_Encoder = 65535 Then Count_Encoder= 1024 ' clock over counter type
If Count_Encoder <= 0 Then Count_Encoder= 0 ' volume control type of count
GoTo End_Interrupt

Count_Up:

Inc Count_Encoder

' the other part of the conditioning, we can use any value from 0 to 65535
' make sure that both parts of the conditioning relate to the same value !!!!
' If you wanted a maximum count of 10000 then change the 1024 value to 10000

'If Count_Encoder > 1024 Then Count_Encoder = 0 ' clock over counter type
If Count_Encoder >=1024 Then Count_Encoder = 1024 ' volume control type
End_Interrupt:

INT1IF = 0 ' clear flag

Get_Out:

Context Restore

Over_Interrupt: ' setup the ports, initialise variables and display, enable the interrupts.

' the encoder A - B output is A = PortB.1 , B = PortB.3
' we dont need a trisb becuase the startup is all input
' leaving the whole ports as inputs is safer so you dont accidently
' connect your encoder output to a PIC® output !
Count_Encoder = 0 ' reset the variable to zero to start with
' you can preset this to a value to use if you like, to form a starting point
DelayMS 200 ' settle period
Cls ' Clear the lcd display

IPEN = 1 ' Enable Priorities for interrupts
PEIE = 1 ' Enable Peripheral interrupts
GIE = 1 ' Global Interrupt Enable

GoTo Display_0_at_startup ' make sure we have something on the display at startup
' Main Program Loop
While 1=1
If Encoder_Now <> Count_Encoder Then ' no need to update the diplay unless anything changed
Encoder_Now = Count_Encoder
Display_0_at_startup:
Print At 0,0,Dec,Encoder_Now," " ' Display the result
EndIf

' Do other things as you require

Wend
' End of main program loop

End ' We should NEVER get here, but just in case

Include "font.inc" ' Font for our GLCD, make it an internal font