Delta-Sigma-ADC in Assembler embedded in PBP, increasing resolution

[selbstdual]

Good evening. I want to increase the code's resolution from 16bit to something deliberate. How do I have to change this code ?



...some code...
ASM
;************************************************* ********************
;* Filename: DeltaSig.asm
;************************************************* ********************
;* Author: Dan Butler
;* Company: Microchip Technology Inc.
;* Revision: 1.00
;* Date: 02 December 1998
;* Assembled using MPASM V2.20
;************************************************* ********************
;* Include Files:
;* p16C622.inc V1.01
;************************************************* ********************
;* Provides two functions implementing the Delta Sigma A2D.
;* InitDeltaSigA2D sets up the voltage reference and comparator
;* in the "idle" state.
;* DeltaSigA2D runs the actual conversion. Results provided in
;* result_l and result_h.
;* See An700 figure 2 for external circuitry required.
;************************************************* ********************
;* What's changed
;*
;* Date Description of change
;*
;************************************************* ********************
#include <p16C622.inc>
cblock
result_l
result_h
counter:2
endc
;
;
;
InitDeltaSigA2D
bsf STATUS,RP0
movlw 0xEC
movwf VRCON
bcf PORTA,3 ;set comparator pin to output
bcf STATUS,RP0
movlw 0x06 ;set up for 2 analog comparators with common reference
movwf CMCON
return
;
; Delta Sigma A2D
; The code below contains a lot of nops and goto next instruction. These
; are necessary to ensure that each pass through the loop takes the same
; amount of time, no matter the path through the code.
;
DeltaSigA2D
clrf counter
clrf counter+1
clrf result_l
clrf result_h
movlw 0x03 ; set up for 2 analog comparators with common reference
movwf CMCON
loop
btfsc CMCON,C1OUT ; Is comparator high or low?
goto complow ; Go the low route
comphigh
nop ; necessary to keep timing even
bcf PORTA,3 ; PORTA.3 = 0
incfsz result_l,f ; bump counter
goto eat2cycles ;
incf result_h,f ;
goto endloop ;
complow
bsf PORTA,3 ; Comparator is low
nop ; necessary to keep timing even
goto eat2cycles ; same here
eat2cycles
goto endloop ; eat 2 more cycles
endloop
incfsz counter,f ; Count this lap through the loop.
goto eat5cycles ;
incf counter+1,f ;
movf counter+1,w ;
andlw 0x04 ; Are we done? (We're done when bit2 of
btfsc STATUS,Z ; the high order byte overflows to 1).
goto loop ;
goto exit
eat5cycles
goto $+1 ; more wasted time to keep the loops even
nop ;
goto loop ;
exit
movlw 0x06 ; set up for 2 analog comparators with common reference
movwf CMCON
return
end
ENDASM

[blainecf]

By deliberate do you mean 8bits, 12 bits, 19bits??? Are you just wanting to know what was implicitly set (by default) that makes this 16 bit? What is your ultimate goal?

bcf

[selbstdual]

Thank you for your question.

Exactly, I want to know how it subdivides in 1024 steps. Then it should be easy to change it to the desired value.

[mister_e]

well i certainely miss something here but, 1024 steps it's 10Bit. you said you want Increase your actual 16Bit resolution.. euh... i'm i wrong or what.

By the way, why using the comparator when a real ADC give you already 10Bit resolution without headache, need few lines of code and no big additional hardware?

[Ingvar]

These lines checks for 1024 passes through the loop and stops if reached.

andlw 0x04 ; Are we done? (We're done when bit2 of
btfsc STATUS,Z ; the high order byte overflows to 1).

All you need to do is change ....

andlw 0x04

..... to .......

andlw 0x02 for 512(9 bits)
andlw 0x08 for 2048(11 bits)
andlw 0x10 for 4096(12 bits)
andlw 0x20 for 8192(13 bits)
andlw 0x40 for 16384(14 bits)
andlw 0x80 for 32768(15 bits)

If you need better resolution it can be done, but needs more changing in the code.

/Ingvar

[selbstdual]

Thank you so far.

In my current application, I need around 750 steps. Surely I could use 1024 steps right now.

I want to change it to the number of steps wanted, but I have not understood the relation yet.

Please explain the math behind your examples.