Dear Sir
In software we can read the registers on the ADC081C027 chip, but we need help understanding the binary data we see. It is not documented in datasheet.
Best regards,
Bogey
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Dear Sir
In software we can read the registers on the ADC081C027 chip, but we need help understanding the binary data we see. It is not documented in datasheet.
Best regards,
Bogey
Hello Bogey,
The description of the internal registers is found in the datasheet, starting on page 17. You can take the binary data you have read from a register and compare it to the description of the register, which will tell you the definition of each bit of the register.
Mike
Hi Milk
The customer have more question descripton as belwo:
We already read the "Conversion Result Register", bits 11:4.
We do not understand the meaning of the bits there.
The datasheet says this is the "result of last conversion", but not anything more.
1. What units is this in?
2. How do we convert this to a voltage level?
Datasheet does not say?
Examples:
When analog input pin is floating, we read a small decimal value (like 3 or 8 -- it varies, usually under 15).
When analog input is connected to ground we always read 0.
When analog input is connected to 0.5V, 1.0V, 1.7V or 2.5V we read apparently random values between 50 and 100 (our reference voltage is 3.3V).
We reboot the setup, and next time the same voltage levels gives 'random' values in a different interval (say 80 and 140).
There is no pattern in the values read and the voltage level supplied.
regards,
Bogey
Hi Bogey,
I have pasted your questions below along with the answers.
>>We already read the "Conversion Result Register", bits 11:4.
>>We do not understand the meaning of the bits there.
The conversion result data is in straight binary format with the MSB at D11. 0V on the input will give 0x00 and VA (which is also VREF for this part) on the input will give 0xFF.
>>The datasheet says this is the "result of last conversion", but not anything more.
When the part is powered on a first conversion is completed and the Conversion result is put in the register. When you read the Conversion Result Register you get this result. That is what "result of last conversion" means, you are not getting the result of the current read. When you do a read of the Conversion Result Register a new conversion is started and after the read this result is put in the Conversion Result Register ready for the next time you read.
>>1. What units is this in?
It is in volts referenced to the VA voltage.
>>2. How do we convert this to a voltage level?
Convert the 8-bit value (DOUT) from binary to decimal. The voltage is V = DOUT * VA / 256.
>>When analog input pin is floating, we read a small decimal value (like 3 or 8 -- it varies, usually under 15).
Correct, the input is floating so it is undefined.
>>When analog input is connected to ground we always read 0.
Correct.
>>When analog input is connected to 0.5V, 1.0V, 1.7V or 2.5V we read apparently random values between 50 and 100 (our reference voltage is 3.3V).
You should get about the following values with a 3.3V reference:
0.5V = 0x27
1.0V = 0x4E
1.7V = 0x84
2.5V = 0xC2
Check the Typical Application Circuit section of the datasheet.
The supply for the ADC needs to be very quiet. You need to have bypass capacitors located close to the pin of the part. All ground connections need to be connected to a common ground plane. You should have a capacitor on the input of the part. You will also need the resistor if you are driving the ADC with an op amp.
Mike