MCP23016 I/O expander

[NavMicroSystems]

Ok, I'm trying to read from the 2nd MCP23016 and it's not working smoothly. I display the word on an LCD, and bits seem to flicker sometimes. When I press a button, the corresponding bit turns on, but there are some 'free games' here and there.

Robert,

we don't want to guess anymore, please post your full code and schematic.

[Demon]

'define LOADER_USED 1
ADCON1 = 7 ' A/D off, all digital

ASM
@ DEVICE PIC16F877, HS_OSC, WDT_OFF, PWRT_ON, BOD_ON, LVP_OFF, CPD_OFF, WRT_OFF, DEBUG_OFF, PROTECT_OFF
ENDASM

define OSC 20

DEFINE LCD_DREG PORTA
DEFINE LCD_DBIT 0
DEFINE LCD_RSREG PORTA
DEFINE LCD_RSBIT 4
DEFINE LCD_EREG PORTB
DEFINE LCD_EBIT 3
DEFINE LCD_BITS 4
DEFINE LCD_LINES 4
define LCD_COMMANDUS 2000
DEFINE LCD_DATAUS 50

DEFINE I2C_SLOW 1
DEFINE I2C_HOLD 1
I2CSCL VAR PortD.1
SDAISW1 VAR PortC.2

LOCGPIO CON $00
LOWWORD CON %0000000000000000

I2CCTRL VAR BYTE
I2CLOCB VAR BYTE
I2CWORD VAR WORD
CTRLIOW CON %01000000
CTRLIOR CON %01000001

GOTO START ' Bypass subroutines

'--------------------------- SUB-ROUTINES ----------------------------

RDISW1:
I2CREAD SDAISW1,I2CSCL,I2CCTRL,I2CLOCB,[I2CWORD]
PAUSE 12
RETURN

'-------------------------- MAIN PROGRAM -----------------------------

START:
PAUSE 2000
LCDOUT $FE,1,"Program start"

CYCLE:
I2CCTRL = CTRLIOW
I2CLOCB = LOCGPIO
I2CWORD = LOWWORD
GOSUB RDISW1
I2CCTRL = CTRLIOR
GOSUB RDISW1
LCDOUT $FE,$94,BIN16 I2CWORD
GOTO CYCLE

END


Circuit coming up.

Robert

[Demon]

Circuit:

Robert

[Demon]

I tried reading from the INTCAP instead of the GPIO with much better results.

Got more tests to do.

EDIT: Nope, not that, nevermind...

Robert

[NavMicroSystems]

Robert,

As I'm not using the MCP23016 I haven't read the entire datasheet.

But looking at your schematic there is one thing that may cause strange effects:

you have switches to VDD, but no PullDown Resistors.
So when the switches are open the MCP's inputs are floating.

(I would prefer to have the switches connected to GND and have PullUps to VDD)

I

[Demon]

ARGH!

Thanks Ralph! I can't believe I missed that. Pull-up resistors is one of those things that I watch out for in all switches.

But I've been so busy learning new stuff on this circuit that I've totally forgotten what I consider to be a basic thing. I was so sure I had misunderstood something in the MCP23016 datasheet, or wired an I2C device improperly, a pull-up resistor never dawned on me.

The circuit works beautifully now.

Robert