Labels, constants & numbers

Labels

A label names a location in your program. Labels must start with a letter, a period, or an underscore, and may optionally end with a colon:

start:
    jp start

message  db "Hello", 0     ; the colon is optional

Local labels

A label that starts with a period (.) is local — it’s scoped to the nearest preceding global label. This lets you reuse short names like .loop without clashing:

delay:
    ld b, 255
.loop:
    djnz .loop        ; refers to delay.loop
    ret

wait:
    ld b, 100
.loop:                ; a different .loop, scoped to wait
    djnz .loop
    ret

You can refer to a local label from elsewhere by its full global.local name (e.g. delay.loop).

Constants

Define a constant with = or EQU:

WIDTH   = 256
HEIGHT  EQU 192
SIZE    = WIDTH * HEIGHT

Constants are compile-time values usable anywhere an expression is allowed.

Number formats

mask    = %00000111
addr    = $8000
screen  = 0x4000
letter  = 'Z'