MCP23016 I/O expander

[Demon]

I am trying to wire an MCP23016 as output; driving LEDs. No matter what I try, no LEDs light up. Any idea what I am missing?

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'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 ' Set LCD data port
DEFINE LCD_DBIT 0 ' Set starting data bit
DEFINE LCD_RSREG PORTA ' Set LCD register select port
DEFINE LCD_RSBIT 4 ' Set LCD register select bit
DEFINE LCD_EREG PORTB ' Set LCD enable port
DEFINE LCD_EBIT 3 ' Set LCD enable bit
DEFINE LCD_BITS 4 ' Set LCD bus size
DEFINE LCD_LINES 4 ' Set number of lines on LCD
define LCD_COMMANDUS 2000 ' Set command delay time in microseconds
DEFINE LCD_DATAUS 50 ' Set data delay time in microseconds

DEFINE I2C_SLOW 1 ' Access I2C device above 8MHz
'DEFINE I2C_SCLOUT 1 ' Set I2C clock line as bipolar
DEFINE I2C_HOLD 1 ' Permit I2C device to hold clock line low

I2CSDA VAR PortC.4 ' Data line
I2CSCL VAR PortC.3 ' Clock line
I2CCTRL VAR BYTE ' I2C chip address
I2CLOC VAR BYTE ' I2C location byte
I2CBYTE1 VAR BYTE ' I2C 8 bit data string
I2CBYTE2 VAR BYTE ' I2C 8 bit data string

GOTO START

ERRORIO:
LCDOUT $FE,$94,"No ACK from I2C device"
RETURN

START: PAUSE 2000 ' Wait for LCD to initalize
LCDOUT $FE,1,"Program start"

' I2C device address: ID A2 A1 A0 R/W
' ---- -- -- -- ---
' 0100 0 0 0 0

I2CCTRL = %01000000
I2CLOC = $06 ' Set location to IODIR register pair
I2CBYTE1 = %00000000 ' Set pins 0-7 as output
I2CBYTE2 = %00000000 ' Set pins 8-15 as output
I2CWRITE I2CSDA,I2CSCL,I2CCTRL,I2CLOC,[I2CBYTE1,I2CBYTE2],ERRORIO
PAUSE 2000

I2CCTRL = %01000000
I2CLOC = $00 ' Set location to GPIO register pair
I2CBYTE1 = %00101010
I2CBYTE2 = %00000000
I2CWRITE I2CSDA,I2CSCL,I2CCTRL,I2CLOC,[I2CBYTE1,I2CBYTE2],ERRORIO

Finish:
LCDOUT $FE,$D4,"Process complete"
end
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Yeah, I just noticed an error in my I2CWRITE comment. I meant pins in the sense of logical pins(GP0.0-GP0.7 and GP1.0-1.7).

I also did some trial & error with the I2C DEFINES, but no luck there. I even increased the PAUSE in case. The program terminates properly, so it seems as if I do get some sort of acknowledgement from the device.

I've triple-checked the wiring a zillion times. I followed the datasheet and placed the RC as specified.

I'm stumped...

Thanks!

Robert

[Melanie]

I don't see you initialising this chip. Last I checked it had twelve registers... let's set them up the way you'd like to see them.... then and only then you can perform I/O.

Have you remembered to GROUND A2, A1 and A0 to match your IOCCTRL Byte?

Have you remembered to leave TP floating?

Have you remembered to GROUND all THREE Vss pins?

Have you remembered Rext and Cext for your external Clock, or alternatively cross-connected it to Fosc of your PIC?

[Demon]

"I don't see you initialising this chip. Last I checked it had twelve registers... let's set them up the way you'd like to see them.... then and only then you can perform I/O."

The default values for all the registers seem to be what I want except for the IODIR register pair. According to the datasheet, we are able to write to both registers in a single write operation. The 1st I2CWRITE is supposed to write all ZEROES to both registers (IODIR0 and IODIR1):

I2CCTRL = %01000000
I2CLOC = $06 ' Set location to IODIR register pair
I2CBYTE1 = %00000000 ' Set pins 0-7 as output
I2CBYTE2 = %00000000 ' Set pins 8-15 as output
I2CWRITE I2CSDA,I2CSCL,I2CCTRL,I2CLOC,[I2CBYTE1,I2CBYTE2],ERRORIO

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"Have you remembered to GROUND A2, A1 and A0 to match your IOCCTRL Byte?"

Yup.

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"Have you remembered to leave TP floating?"

Yup.

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"Have you remembered to GROUND all THREE Vss pins?"

Yup.

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"Have you remembered Rext and Cext for your external Clock, or alternatively cross-connected it to Fosc of your PIC?"

Yup, on the RC connection. I wanted to try your 2nd suggestion, but I can't see an Fosc pin on the 16F877.

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I've even connected all 16 I/O pins to LEDs, so I can easily see what is happening.

Robert

[Demon]

Is there any particular reason why MicroChip would NOT include in the datasheet for the MCP23016 a little diagram of pull-up resistors on the data and clock lines?

Who knows how long this has been working...

Robert

[Demon]

Hmm, I have a feeling the pull-up resistor is more a requirement for the PIC 16F877 than for the MCP23016...

Robert

[Melanie]

4K7 pull-up's ARE required on the I2C lines.