Address half PORTB

[sifran]

Hi everyone!
I have PORTB on a DSPIC 33F which is connected to two 8 bit DACs, one on PORTB 0-7 and the other on PORTB 8 - 15.
How can I directly access, with one intruction, the two halfs of the port as if they were two 8 bit ports?

Thank you very much!

[anikolic]

Hi,
Can you specify what dsPIC33 are you using? This family of microcontrollers has 16-bit operations, so all assembly lines use 16-bit word operands, unless specified to use byte operands, by extending asm directives with .B suffixes. This means that if you write, for example:

Code: Select all

unsigned int PORTVal;

void main(){
  PORTVal = 0x0000;
  PORTB = 0x1234;
  PORTVal = PORTB;
}

assembly equivalent generated by the compiler would be:

Code: Select all

;void main(){
;PORTVal = 0x0000;
	MOV	#0, W0
	MOV	W0, _PORTVal
;PORTB = 0x1234;
	MOV	#4660, W0
	MOV	W0, PORTB
;PORTVal = PORTB;
	MOV	PORTB, W0
	MOV	W0, _PORTVal

Of course, you must use two assembly instructions to copy one 16-bit value from one register to another, by using W0 working register as a mediator. Only W registers can be copied directly in a single cycle with MOV commands, but other registers must be copied using two clock cycles.
If this is not the answer to your question, please rephrase and paste a piece of commented code that gives you trouble, and I'll do my best to help.

Best regards,
Aleksandar

[sifran]

Thank you Aleksandar, the machine is Dspic33fj128G710, I am not so practical with assembly, I will try to implement the code you suggested.
My question was maily related ti MikroC code.