I2C and MCP23016

[Darrel Taylor]

Since you are using an 18F4550, it means you are using MPASM as the assembler.
So, DEFINE i2c_hold 1 needs to be Uppercase.

You can read back every register except one (INTCAP). I do not know what fails, read or write

Not sure what you mean here. The INTCAP? registers are read-only.

Also not sure what you are trying to do with the port.
You write all 1's to the output latch OLAT1, then set all but 1 pin to input IODIR1, then write to GP1 which actually writes to OLAT1 again. Doesn't make sense.

What is it you're trying to do, and what's not working.

[keymuu]

Since you are using an 18F4550, it means you are using MPASM as the assembler.
So, DEFINE i2c_hold 1 needs to be Uppercase.

Not sure what you mean here. The INTCAP? registers are read-only.

Also not sure what you are trying to do with the port.
You write all 1's to the output latch OLAT1, then set all but 1 pin to input IODIR1, then write to GP1 which actually writes to OLAT1 again. Doesn't make sense.

What is it you're trying to do, and what's not working.

Thank you Darrel!

I changed it, so now I have DEFINE I2C_HOLD 1...
but that did not change anything.

With INTCAP I just wanted to say that it is the only register that is read-only, besides it was kind of irrelevant from me to mention that in the first place

The final goal is to use the device as an input extender, that is only inputs. However, one should also be able to read and write all registers, except one. Nothing seems to work, as earlier told, I can't tell if it is the write or read that fails. I have tried all kind of values and also changing the sequence of those three initializing lines but without any sign of life. Well, of course maybe some kind of quiet life when not the error label is activated.

What values would you suggest to use in the initialization section and what sequence would you use for those three init lines?

[Darrel Taylor]

I think it's probably working, but you don't realize it.

In your code, the only thing you're reading is GP1, and prior to that it writes to GP1, so you're thinking you should read the same value back.

But when you write to GP1, the value is actually written to OLAT1.
Reading GP1 reads the state of the pins, not what was written to GP1.
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[keymuu]

I think it's probably working, but you don't realize it.

In your code, the only thing you're reading is GP1, and prior to that it writes to GP1, so you're thinking you should read the same value back.

But when you write to GP1, the value is actually written to OLAT1.
Reading GP1 reads the state of the pins, not what was written to GP1.
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Thanks, I really hoped you were right, but sorry...
I tested it with the following code:
Loop:
I2Creg = OLAT1 : I2Cbyte = $ff : gosub writeioextender: pause 20
I2Creg = IODIR1 : I2Cbyte = $ff : gosub writeioextender: pause 20

I2Creg = olat1 : gosub readioextender: pause 20
LCDOUT hex2 ioebyte, " "
I2Creg = gp1 : gosub readioextender: pause 20
LCDOUT hex2 ioebyte, cmd,home1
if onoffpressed = 1 then powerout = 0
goto Loop

I have a button on GP1.0 (pin 2) that is pressed or not, on the LCD one can only see 00 00, nothing else. I think this demonstrates that you can not write OLAT1 or read it, it also shows that a button press does not come through, or perhaps the GP1 is not initialized correctly. Tested also to write IODIR1 first but with the same result...

How should one initialize the chip with all pins as inputs?

[Darrel Taylor]

When you get all 0's, it usually means one of two things.

1) The SDA,SCL pins still have the analog mode enabled.

2) There aren't any pull-ups, or they pull-down.

If you have a voltmeter, check the voltage on the SDA,SCL pins.
They should be above 4V when no data is being transfered.

But I'm betting on analog mode.
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[keymuu]

When you get all 0's, it usually means one of two things.

1) The SDA,SCL pins still have the analog mode enabled.

2) There aren't any pull-ups, or they pull-down.

If you have a voltmeter, check the voltage on the SDA,SCL pins.
They should be above 4V when no data is being transfered.

But I'm betting on analog mode.
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As said in post 1#, both (SCL and SDA) are pulled up with 2 2k2 resistors, one for each. So when the lines are inactive you can measure 4,98V there, so that suggest also that the problem has to be somewhere else. I have also looked with an oscilloscope on the active signals, but being not so familiar with the inner live of the I2C protocol, can't tell if there would be something wrong, to me they look "normal". From the clock line I could calculate a clock frequency of something around 65kHz +/-20%. Is that OK?

[Darrel Taylor]

Then it must be 1).

Put this line at the top of your program.

ADCON1 = $F ; set all pins to digital
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