MCP3901 and PIC18F46K22

Dear All,

I'm working on a project where I want to read DC Battery charging discharging Current from a shunt. For that I'm using MCP3901(it has differential input plus 24 bit resolution) and PIC18F46K22. I'm using Hi-Tech compiler demo and its SPI library. Reading and writing in to all internal registers is going well but when i read ADC Data registers (applied voltage at inputs is 5V ref is 2.37V) it should give me 0x7FFFFF i.e. full scale reading. But its giving me 0x7F7F7F. What should be the problem.

Kindly help me out.

That MCP3901 is a very complicated chip.
I have no idea what some of its settings do !
I'd advise you to use a simpler device, or use the ADC built into the 18F46K22.

A 10 bit resolution may not seem much compared to 24,
but I believe it is good enough in practise.

The 18F46K22 has many channels, so you could scale inputs with external
amplifiers to get good results.

are you sure your read is working properly? I mean you're not getting first byte again and again.

[Topic moved to PIC Microcontroller Discussion Forum]

Sir,

I was doing like this

MCP3901_CS = 0;
WriteSPI1(0x01);
TempData = ReadSPI1( );
TempData <<= 8;
TempData |= ReadSPI1( );
TempData <<= 8;
TempData |= ReadSPI1( );
MCP3901_CS = 1;

and my problem solved by doing like this

MCP3901_CS = 0;

WriteSPI1(0x01);
TempData = ReadSPI1( );
TempData <<= 8;
MCP3901_CS = 1;

MCP3901_CS = 0;

WriteSPI1(0x03);
TempData |= ReadSPI1( );
TempData <<= 8;
MCP3901_CS = 1;

MCP3901_CS = 0;

WriteSPI1(0x05);
TempData |= ReadSPI1( );

MCP3901_CS = 1;

I really do not understand why are you reading register 1, 3 and 5 register 1 belongs to CH0 and 3,5 belongs to CH1. I think you should read chapter 6.7 of datasheet for reading in continuous mode.

Ajay Sir,

CHannel 0 Register is 24 Bit. it register address is from 0x00 to 0x02. To read any register we have to send command with first bit 1(Read Bit). so to read CH0 register address will be 0x01 (MSB)
0x03(Middle Byte)
0x05(LSB).

I get it now.. Did not read that part, sorry for misunderstanding.