help with rotary encoder, code

sejasti123

I have an incremental encoder and I try it using the basic stamp.
The tests went well but I have doubts regarding a line of code.

' =========================================================================
' {$STAMP BS2}
' {$PBASIC 2.5}

'

---

[ I/O Definitions ]

---

' A Output Connects To P0
' B Output Connects To P1


'

---

[ Variables ]

---

oldBits VAR Nib ' Previous State Of I/O Pins 0 - 3
newBits VAR Nib ' Current State Of I/O Pins 0 - 3
direction VAR Bit ' Direction Encoder Is Turned
counter VAR Word ' Counter


'

---

[ Initialization ]

---

OUTS = %0000000000000000 ' Set All Output Pins Low
DIRS = %1111111111111100 ' I/O Pins 0 - 1 Inputs

newBits = INA & %0011

'

---

[ Program Code ]

---

Main:
DO
' newBits = INA & %0011 ' Get State Of I/O Pins 0, 1
' IF newBits <> oldBits THEN ' Have Bits Changed?
' direction = newBits.BIT0 ^ oldBits.BIT1
counter = counter - 1 + (2 * direction)
DEBUG HOME, DEC5 counter ' Show New Counter On DEBUG Screen
oldBits = newBits ' Update oldBits
' ENDIF
LOOP
'STOP


What does INA mean?

Why changing it to INB or INC nothing happens and the program is still normal.

Phil Pilgrim (PhiPi)

INA is a pseudo-variable that returns the state of the lower 4 I/O pins, packed as 4 binary bits, P0 being the least-significant. If the pin is high, its bit will return as a 1; otherwise, 0.

-Phil

tomcrawford

INA means Input pins 3..0. INB means 7..4. And so on. The program would still compile, but would be using the wrong inputs.

sejasti123

Thank you so much guys,