Can't write (or read) byte to MCP79411

[JerryR]

Hello group:

Hope someone can help me with this issue.

I'm using PCWH v5.121 and the driver for the MCP79411 as published in the code library. Excellent work by Daniel Pechmann !

I'm attempting to adjust the ADR_CAL register (0x08) without success. Time functions all work correctly, however. It appears that I can't either read or write to any particular register. After a write, I always receive 0xA5.

As far as hardware, pretty typical. 2.2Kohm pull-ups on both SDA and SCK lines. No other devices share the I2C port. Using hardware I2C port on PIC16F1619.

Here's the test code:

[Ttelmah]

An issue straight away. The rtc_read_byte function is for reading the
rtc registers, which are BCD coded. Not a binary register like the calibration
one. To read the value from that you'd need to code your own version
of the read function without the bcd conversions. May not be the problem
but needs to be fixed.

[JerryR]

Hi Ttelmah:

Yes, understand that, so not an issue to retrieve non BCD data. However, polling any register with this code returns 0xA5. I'm wondering if I'm actually setting correct information in a register with the write byte routines, but not reading a register correctly.

Can't believe no one has ever noticed this before.

Thanks for your help

[JerryR]

Hi Ttelmah:

Solved:

Yes, you were certainly right that reads, as his code provided, were converted to BCD. However, both reads and writes were addressing the EEPROM region in the MCP79411, not the SRAM/RTCC region as I required to write to.

Simply closely examining the data sheet and writing my own code to address the SRAM/RTCC area fixed the issue. Thanks for your kind assistance.

All the best

[Ttelmah]

Well done. I didn't know this chip, but looking at the code spotted the
BCD conversion, so thought I'd point that out.
Separately, though it defaults to 0, I'd probably explicitly clear the multiplier
bit in the control register, just to 'make sure'......
Flag the thread as solved please.

Recently CCS has been the subject of a rather heavy DOS attack, and
this forum was caught in the periphery of this. Hopefully they seem to be
getting on top of this and things should be going back to normal.

[JerryR]

Thanks Ttelmah.

Yes, will follow up as you suggest.

Also saw the DOS on the forum website. I don't see what they get from doing this and I'm sorry it has been an issue on such a valuable resource.

Again, many thanks for your interest and keep up you valuable work.

[Ttelmah]

The point about 'flagging as solved', is that as the thread creator, edit the title,
so it has [solved] in it. You have to do this. Others can't.

On the DOS, it was CCS themselves that had the biggest hit. The forum
sort of just got caught as a link from the CCS site. Probably just an idiot
playing with an AI (it is possible now to do quite powerful DOS attacks
using these). If it was a DDOS attack (lots of sources), it may possibly
have been done using an automated script Why?. I don't know if there
is an answer. Why do people commit vandalism is a similar question.....