Question about how Z pointer works

[Navid T]

Question about Z pointer

Hello
I wrote this code To test how pointer works. I want to Write $4 from Address $50. This Program works Properly But it doesn’t work when I write 50H in Z Register.!!!
Why should I use 1 bit shift left in Pointer register? (Z) I want to reade from 50H but its Twice in Z.
-----------------------------------------------------------------
#include "m32def.inc"
.ORG 0X0000
SETUP:
LDI R16,HIGH(RAMEND)
OUT SPH,R16
LDI R16,LOW(RAMEND)
OUT SPL,R16
LDI R16,$FF
OUT DDRB,R16
MAIN:
LDI R31,HIGH(0X50<<1)
LDI R30,low(0x50<<1)
LPM R16,Z
OUT PORTB,R16
RJMP MAIN
.ORG 0X50
.DB $4
-------------------------------------------------------------------
Best regards

 

[Eugen_E]

Re: Question about Z pointer

It's because the program memory is organized on words - 2bytes, because this is the instruction format for AVR.
LPM will access the memory byte by byte, so the address should be multiplied by 2. LPM will address the LSB from an even (lower) address and MSB from odd (higher) address.