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'[PIC]: PIC16x84 and MAX1111 - help!'
2001\06\17@182957 by Philip Pemberton

   I've now got my LCD and my iButtons working fine (the LCD had a few
missing pixels - cured by tightening up the ground clips on the bottom of
the panel), thanks to some code included in the PIC Tutorial (by John
Becker, published in Everyday Practical Electronics magazine). Donnie James
has also sent me a fixed version of my PIC LCD routines that I'm going to
use instead of the PICtutor ones.
   Now I'm onto my second challenge - getting a Maxim MAX1110 or MAX1111
ADC to communicate with a PIC16x84. I've gone over the timing diagrams in
the datasheet numerous times, but I still can't get any data out of the
MAX111x... The code is rather large (a few hundred lines) so I'm only
sending it to those who request it, rather than clogging up the mailing
list. Has anyone got some (working) MAX111x ADC code they wouldn't mind
sharing with me? These ADCs are a pain in the neck to work with - even when
you follow the timing diagrams!

Thanks in advance.


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2001\06\27@173449 by Morgan Olsson

picon face
*rant warning*

I don´t know about MAX1110/MAX1111 but maybe they are like the MAX110/111, that wrecked one project for me... ARGH!

Theese MAX11x are commanded and also reset, ofset, gain adjust, calibrated,etc using the SPI to talk to them.

The data sheet tells there are some undocumented commands the user shall not send.

In an noisy environment, especially at startup/reset/brownout etc it is not easy to know what will hit the bus.  Also those chips have no reset pin, can only be reset by all power pins zeroed.  So when something pulls the reset to the CPU in the middel of a SPI session the MAX may interpret that as one of the undocumented commands!  And the undocumneted commands are test commands...

There is the NOP command that in the doc is said to reset the chip.
Unfortunately that is false.  There is at least one test command that start a test that never ends, and what is most evil is that the chip then sends data on the SPI bus even with the chip select pin inactive, and so destroying all communication between other devices on the bus!!  In the machine in which I implemented the MAX that was catastrophic.

Intil I got that one nailed i worked weeks with trying to reproduce the lockup and rewrote a large port of my program twice!

No more Maxim A/D for me, thank you.

BTW, there is also a bug in earlier versions of Linerar Technolgy LTC2400 A/D: something about when using it in polled mode (polling Busy flag) it sent the result shifted one bit of it got ready at the same time we poll the flag.  Also that took a time to find.  I now have a PCB with a PIC and an old and newer LTC2400 and can prove it.

I have ranted on theese chips on the list when i was having thoose problems two years ago or so, look in the PIC archives  if you want to know more.

Some guy i met in this list had similar problem with another MAX A/D, and went on the route of total power down between readling.

Maxim confessed the bug after weeks of mailing, LT say they have never changed the interface, but i have a PIC with red and green led then can tell old ones from new ;).

It is OK to make bugs, but only if they are described in erratas!!
Or at least handled properly when reported!

Theese guys do marvellous analog parts, but I´ve learnt the hard way to be very careful and test everything with the digital side!


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