adc,   add,   adiw,

adc, ( Rd Rr --)

Add with Carry

Adds two registers and the contents of the C Flag and places the result in the destination register Rd.

add, ( Rd Rr --)

Add without Carry

Adds two registers without the C Flag and places the result in the destination register Rd.

\ Increment 24 bit value until result is zero
: testuntil
  [ #16 #0 ldi, ]
  [ #17 #0 ldi, ]
  [ #18 #1 ldi, ]
  [ begin, ]
  [   #16 #6 add, ] \ R6 contains 1
  [   #17 #5 adc, ] \ R5 contains 0
  [   #18 #5 adc, ]
  [ eq, until, ]    \ until R18 is zero
;

adiw, ( Rw k6 --)

Add Immediate to Word

Adds an immediate value (0 - 63) to a register pair and places the result in the register pair. This instruction operates on the upper four register pairs, and is well suited for operations on the pointer registers.

This instruction is not available in all devices. Refer to the device specific instruction set summary.