Attribute Writing

Overview

The Spectrum’s attribute system lets you colour 8x8 character cells without drawing pixels. Each attribute byte controls foreground (ink), background (paper), brightness, and flash. This is the fastest way to create colourful displays and is the basis for many classic Spectrum game graphics.

Code

; =============================================================================
; ATTRIBUTE WRITING - ZX SPECTRUM
; Direct manipulation of attribute memory
; Taught: Game 1 (Ink War), Unit 1
; CPU: ~30 cycles per cell | Memory: ~40 bytes
; =============================================================================

ATTR_BASE   equ     $5800           ; Start of attribute memory (768 bytes)

; Attribute format: %FBPPPIII
; F = Flash (0=off, 1=flashing)
; B = Bright (0=normal, 1=bright)
; P = Paper colour (0-7)
; I = Ink colour (0-7)

; Colour values
BLACK       equ     0
BLUE        equ     1
RED         equ     2
MAGENTA     equ     3
GREEN       equ     4
CYAN        equ     5
YELLOW      equ     6
WHITE       equ     7

; Example attributes
ATTR_WHITE  equ     %00111000       ; White paper, black ink
ATTR_FLASH  equ     %10111000       ; White paper, black ink + FLASH
ATTR_BRIGHT equ     %01111000       ; White paper, black ink + BRIGHT

; Set attribute at row, column
; Input: B = row (0-23), C = column (0-31), A = attribute value
set_attribute:
    push    af                  ; Save attribute value

    ; Calculate address: ATTR_BASE + row * 32 + column
    ld      a, b
    ld      l, a
    ld      h, 0
    add     hl, hl              ; *2
    add     hl, hl              ; *4
    add     hl, hl              ; *8
    add     hl, hl              ; *16
    add     hl, hl              ; *32
    ld      a, c
    add     a, l
    ld      l, a
    ld      bc, ATTR_BASE
    add     hl, bc              ; HL = attribute address

    pop     af                  ; Restore attribute value
    ld      (hl), a             ; Write attribute
    ret

Fill a rectangular area:

; Fill rectangle with attribute
; Input: B = start row, C = start column
;        D = height, E = width, A = attribute
fill_attributes:
    push    af

.row_loop:
    push    bc
    push    de

.col_loop:
    pop     de
    pop     bc
    pop     af
    push    af
    push    bc
    push    de

    call    set_attribute

    inc     c                   ; Next column
    dec     e
    jr      nz, .col_loop

    pop     de
    pop     bc
    inc     b                   ; Next row
    dec     d
    jr      nz, .row_loop

    pop     af
    ret

Fast row fill (optimised):

; Fill entire row with attribute
; Input: A = row (0-23), E = attribute value
fill_row:
    ld      l, a
    ld      h, 0
    add     hl, hl
    add     hl, hl
    add     hl, hl
    add     hl, hl
    add     hl, hl              ; HL = row * 32
    ld      bc, ATTR_BASE
    add     hl, bc              ; HL = start of row in attributes

    ld      b, 32               ; 32 columns
.loop:
    ld      (hl), e
    inc     hl
    djnz    .loop
    ret

Trade-offs

Aspect	Cost
CPU	~30 cycles per cell
Memory	768 bytes for full screen
Limitation	8x8 cell resolution only

When to use: Board games, puzzles, status displays, any game using character-cell graphics.

When to avoid: When you need pixel-level colour control (not possible on Spectrum).

Attribute Memory Layout

$5800-$581F: Row 0  (columns 0-31)
$5820-$583F: Row 1
$5840-$585F: Row 2
...
$5AE0-$5AFF: Row 23

Total: 768 bytes (24 rows x 32 columns)

Colour Reference

Value	Normal	Bright
0	Black	Black
1	Blue	Bright Blue
2	Red	Bright Red
3	Magenta	Bright Magenta
4	Green	Bright Green
5	Cyan	Bright Cyan
6	Yellow	Bright Yellow
7	White	Bright White

Related

Patterns: Game Loop (HALT)

Vault: ZX Spectrum