Hello all,

I am wrote a program which
* writes a byte to input of PCF8591. The analog output is connected to the AIN2 (channel 2) of the same.
* Then the digital output after A to D conversion is read back through I2C bus.
* The values Written to and Read from the DAC/ADC are displayed on LCD for verification.

The aim of the program is to perform a test of the IC connected to P89V664 and display the test result("test fail" or "test pass") on the lcd, to ensure proper (hardware ) setup.


When a '0' is written to DAC a decimal '37' is read from the ADC. For any change in DAC input the ADC value read changes proportionately. I calculated the DAC and ADC outputs as given in the datasheets but the values don't match. [Vagnd = Vdgnd = 0V, Vref = 4.096V].

I want to know:
* What should I do to test the IC.
* Is any better way to perform a self test on the IC?

I am working with P89V664 controller and SDCC compiler. The I2C protocol is implemented by bit banging.

I'd greatly appreciate any comments and suggestions.
Thanks in advance