ADS1256 analog to digital converter

I'm having a real heck of a time with this chip, the TI ADS1256 A to D
converter. Has anyone else here programmed this device before with a uC
. I am using an atmel atmega 162 . All of my outputs look alive and
well, and the ADC sends back semi random data when I attempt to just
read a configuration register. If anyone here has example code (pseudo
code, assembler, c, any processor) I would be relieved to just see some
example of the proper sequence or timing. I've been through the data
sheet several times and have cut back from a complete configuration and
data acquisition to a very simple "what's in this register" and still
don't have it working. TI doesn't have any examples of coding on their
website as far as I can tell. I'm truly at a loss here, as the signals
all look fairly clean (SPI signals), as far as I can tell I'm sending
the right sequences and still I just get random gibberish from the
chip. Thanks!

fenriswolfnews@hotmail.com wrote:
> I'm having a real heck of a time with this chip, the TI ADS1256 A to D
> converter. Has anyone else here programmed this device before with a uC
> . I am using an atmel atmega 162 . All of my outputs look alive and
> well, and the ADC sends back semi random data when I attempt to just
> read a configuration register. If anyone here has example code (pseudo
> code, assembler, c, any processor) I would be relieved to just see some
> example of the proper sequence or timing. I've been through the data
> sheet several times and have cut back from a complete configuration and
> data acquisition to a very simple "what's in this register" and still
> don't have it working. TI doesn't have any examples of coding on their
> website as far as I can tell. I'm truly at a loss here, as the signals
> all look fairly clean (SPI signals),
what kind of SPI signals,
there are 4 or 8 different definitions of SPI,
regarding on which clock edge data should be valid etc.
Even the same manufacturer (i.e. TI) uses different SPI definitions
for different devices !!

Stef Mientki

  as far as I can tell I'm sending
> the right sequences and still I just get random gibberish from the
> chip. Thanks!
> 

TI just specifies the timing and voltages. They don't specify a "type"
of SPI. I am meeting all the timing diagrams and specs in the document
as far as I can tell. I'm doing the proper significant digit order as
well. I really could benefit from sample code if anyone has any. I'm
doing things in the proper order as well as I can discern from the
ADS1256 manual. However, the manual doesn't contain a single example of
a proper end to end timing diagram or configuration sequence or data
reads like the other ADC's I've used on this project. I've done SPI
interfaces with no problem before. I think this problem lies more in
configuration sequence or my misunderstanding of the proper sequence of
events to get the chip up and going.


Stef Mientki wrote:
> fenriswolfnews@hotmail.com wrote:
> > I'm having a real heck of a time with this chip, the TI ADS1256 A to D
> > converter. Has anyone else here programmed this device before with a uC
> > . I am using an atmel atmega 162 . All of my outputs look alive and
> > well, and the ADC sends back semi random data when I attempt to just
> > read a configuration register. If anyone here has example code (pseudo
> > code, assembler, c, any processor) I would be relieved to just see some
> > example of the proper sequence or timing. I've been through the data
> > sheet several times and have cut back from a complete configuration and
> > data acquisition to a very simple "what's in this register" and still
> > don't have it working. TI doesn't have any examples of coding on their
> > website as far as I can tell. I'm truly at a loss here, as the signals
> > all look fairly clean (SPI signals),
> what kind of SPI signals,
> there are 4 or 8 different definitions of SPI,
> regarding on which clock edge data should be valid etc.
> Even the same manufacturer (i.e. TI) uses different SPI definitions
> for different devices !!
>
> Stef Mientki
>
>   as far as I can tell I'm sending
> > the right sequences and still I just get random gibberish from the
> > chip. Thanks!
> >

>>   as far as I can tell I'm sending
>>> the right sequences and still I just get random gibberish from the
>>> chip. Thanks!
>>>
> 

I just tried to connect the ADS1255 to a PIC,
and indeed me too had troubles.
Problem was caused by parameter t6,
which I've never seen so bad in any other SPI device ;-)

In case it might help,
below is my test code for a PIC, written in JAL.

succes,
Stef Mientki


-- initialization of the SPI port
-- ADS1255 / ADS1256 @ 7.68 MHz
-- SPI clock t1-max = 4tclock = 2 MHz
const SPI_clock = target_clock / 16      -- 20Mc/16 = 1_250_000
const SPI_device_has_DIO         = false -- if device has combined 
data-IO !!
-- from figure 1 at page 6
const SPI_clock_idle             = low
-- Din is defined at the falling clock edge,
-- setup time t4-minimal = 50 nsec
-- hold time t5-minimal = 50 nsec
const SPI_master_out_active_edge = falling_edge
-- Dout is changed on rising edge, so sampling should be on falling edge
-- propagation delay t7-max = 50 nsec
-- hold time t8-min = 0 nsec
const SPI_master_in_active_edge  = falling_edge


-----------------------------------------------------------------------------
-- Read IO
-----------------------------------------------------------------------------
function ADC24_IO return byte is
var byte data
   spi_send_mssp(_ADS1256_cmd_read_regs | _ADS1256_regs_io)
   spi_send_mssp( 0 )
   delay_10us( _ADS1256_T6_10usec )  <<<=== T6  VERY IMPORTANT
   spi_read_mssp( data )
   return data
end function
-----------------------------------------------------------------------------


-- the main test program, IO should read as 0xE1
forever loop
   ADC24_IO
   Serial_HW_write(ADC24_IO)
   delay_100ms(5)
end loop

Stef Mientki wrote:
>>>   as far as I can tell I'm sending
>>>> the right sequences and still I just get random gibberish from the
>>>> chip. Thanks!
>>>>
>>
> 
> I just tried to connect the ADS1255 to a PIC,
> and indeed me too had troubles.
Another phenomena, I couldn't find in the datasheets:
when an (auto-?) calibration is done,
you've to wait till RDY becomes low,
before issuing any other command,
otherwise it will not be recognized.

This also implies that when auto-calibrate is turned on,
all commands like gain setting, frequency change, buffer etc,
which will cause an automatic selfcalibrate,
you too have to wait !!

Stef Mientki