Can I use the PIC 18F2550 with a DAC 12bits (MCP4822)

[macmmt]

Hello,

I found a circuit that sends data from pic dsPIC30f2012 (that pic has a resolution of 16 bits) to a DAC 12 bits (MCP4822) . My question is if I can use the SPI Module of a pic 18f2550 of 8 bits to send data to the DAC 12 bits. Can I do that or I just have to have the other PIC.


Thanks for your help.

 

[nsaspook]

Hello,

I found a circuit that sends data from pic dsPIC30f2012 (that pic has a resolution of 16 bits) to a DAC 12 bits (MCP4822) . My question is if I can use the SPI Module of a pic 18f2550 of 8 bits to send data to the DAC 12 bits. Can I do that or I just have to have the other PIC.


Thanks for your help.

You send the data in 2 8bit words.

REGISTER 5-1:    WRITE COMMAND REGISTER FOR MCP4822 (12-BIT DAC)
  W-x   W-x W-x  W-0  W-x W-x W-x  W-x  W-x  W-x W-x    W-x  W-x W-x W-x W-x
        —   GA  SHDN  D11 D10 D9   D8   D7   D6   D5    D4    D3 D2  D1  D0
  A/B
 bit 15                                                                  bit 0
REGISTER 5-2:   WRITE COMMAND REGISTER FOR MCP4812 (10-BIT DAC)
  W-x   W-x W-x  W-0  W-x W-x W-x  W-x  W-x  W-x W-x    W-x  W-x W-x W-x W-x
  A/B   —   GA  SHDN  D9  D8  D7   D6   D5   D4   D3    D2    D1 D0   x   x
 bit 15                                                                  bit 0
REGISTER 5-3:   WRITE COMMAND REGISTER FOR MCP4802 (8-BIT DAC)
  W-x   W-x W-x  W-0  W-x W-x W-x  W-x  W-x  W-x W-x    W-x  W-x W-x W-x W-x
        —   GA  SHDN  D7  D6  D5   D4   D3   D2   D1    D0     x  x   x   x
  A/B
 bit 15

https://www.electro-tech-online.com/custompdfs/2010/05/22249A.pdf

 

[macmmt]

Thanks for your reply. As far as I know, the SPI Module of the PIC 16F877A can just send one 8bit word per time. How would you send two words of 8 bits together?

Thanks.

 

[nsaspook]

Thanks for your reply. As far as I know, the SPI Module of the PIC 16F877A can just send one 8bit word per time. How would you send two words of 8 bits together?

Thanks.

16 bits register, send the high 8 bits first, low 8 bits second (or whatever way the device wants).

unsigned char CMD[2],ctrl; // bits 7-4 control bits in ctrl
unsigned int data; // 12 bit data
/* set ctrl config bits */
CMD[0] = (unsigned char) (((data & 0x0F00) >> 8)|ctrl);
CMD[1] = (unsigned char) (data & 0x00F0); // lose the last four bits for 8 bit ADC

You could also use pointers.

 

[Mikebits]

The MCP4822 does not use dual byte mode so above mentioned suggestion will not work. When you send to the MCP4822 simply truncate the 4 LSB's. In other words, send 12 bits ignoring the last 4 LSB.

 

[macmmt]

Thanks Mikebits,

I need to send the 16 bits, the one of 4 bits of control will allow me to select OutA or OutB. The question is how would u send the 16 bits. The SPI module wont work since it just have 8 bits. Could u explain how would the PIC C code be?

 

[nsaspook]

The MCP4822 does not use dual byte mode so above mentioned suggestion will not work. When you send to the MCP4822 simply truncate the 4 LSB's. In other words, send 12 bits ignoring the last 4 LSB.

My bad, It takes 16 bit transfers.
Fixed above code.

 

[nsaspook]

Thanks Mikebits,

I need to send the 16 bits, the one of 4 bits of control will allow me to select OutA or OutB. The question is how would u send the 16 bits. The SPI module wont work since it just have 8 bits. Could u explain how would the PIC C code be?

Assert the chip Enable.
put byte 1 in the SSP register.
wait for the byte to leave.
put byte 2 in the SSP register.
wait for the byte to leave.
De-assert the Chip Enable.