may i use less bits for the ADC?

[belinda_sg]

If my MCU is 10-bit ADC up, but i only want to use for 4-bit ADC, can i do that? and what should i do?

thx for ur kind help

 

[ivancho]

Well what you need to do is divide by 64 the ADC result and then you have a 4-bit number from the convertion.

So lets say your Reference Voltage is 5V and with your 10-bit ADC you get a resolution of 4.88mV increments.
For Example: 3.5V will yield a 716.

If you were to have a 4-bit ADC your resolution would be of 0.3125V increments (assume again a Vref=5V)
So a 3.5V would yield a 11

If you were to take the 10-bit convertion put it into a variable and divide by 64 you will have the equivalent to a 4-bit ADC.

716/64 = 11 Remember that this is all integer math and any floating point is just lost.

Ivancho

 

[crust]

If it is a parallel output ADC, you can just wire up the top 4 bits. For instance, only connect your micro to data bits 9:6. Leave the others floating.

If you read the data into a variable (from an integrated part, etc), just bit shift the data by 6 bits.

int x;
x = readadc();
x = x >> 6;

// now x is a 4 bit ADC.

 

[Nigel Goodwin]

It's even easier than that, you can set the 10 bit A2D so that the highest 8 bits are in ADRESH and the lowest 2 are in ADRESL. This allows you to only use ADRESH as an 8 bit A2D.

Simply SWAPF the top and bottom nibbles over, and ANDLW it with 0x0F to mask off the upper 4 bits - result a 4 digit A2D result in the lower nibble of W.

So it looks like this:

SWAPF ADRESH, w
ANDLW 0x0F