Change text color in Z80 assembly for Amstrad CPC 464

Question

I am trying to code this program, similar to game: "The Typing of The Dead" in Amstrad CPC 464 using Assembly language for the Z80 processor.

The program consists in when you see a string of characters like a word in the screen in yellow, you have to typing exactly as shown. If you type right, the string changes to light blue and continues the game. If you type wrong, the string changes to red hyphens and appears "game over".

I am using the firmware from Amstrad CPC 464 such as this link:

http://www.cantrell.org.uk/david/tech/cpc/cpc-firmware/firmware.pdf

I have some code painting the characters pixel by pixel in the screen but I want to use the firmware to write the characters. There is a way to do this?

I guess that is possible using video modes, pen and inks instructions from firmware but I don't understand enough to use.

this is my code painting pixel by pixel (using WinApe):

org &4000
run &4000
readkey equ &BB1E 

;; START PROGRAM
;; cls
call &bc14
;; initial position video mem.     
ld hl, #c000
;; paint char_a_yellow  
ld bc, char_a_yellow 
;; times to follow rows
ld e,#08
call looph
call wait_typing 
jr $
;; END PROGRAM
;;
;; ROUTINES
looph:
  ;; Times to inc l (cols)
  ld d, #02
  ;; save memory video position to stack
  push hl
  call paintpix
  ;; fetch memory video position from stack
  pop hl
  ld a, h
  ;; adds #08 to next row
  add a,#08
  ld h,a
  dec e
jr nz,looph
ret
;;
paintpix:
  ld a, (bc)
  ld (hl),a
  inc l
  inc c
  dec d
  jr nz, paintpix
ret
;;
wait_typing:
  ;; loads in a value of 'a' character
  call &bb18
  ;;and a       ;;Reset  flag carry
  ld b, #61
  sub b
  jp z,typing_right
  ;;and a       ;;Reset flag carry
  ld b, #61
  sub b
  jp nz,typing_wrong
 ret
 ;;
 typing_right:
  ld hl, #c000
  ld bc, char_a_blue 
  ;; times to follow rows
  ld e,#08
  call looph 
 ret
 ;;
 typing_wrong:
  ld hl, #c000
  ld bc, hyphen_red 
  ;; times to follow rows
  ld e,#08
  call looph 
 ret
 ;;
 ;; CHARS BY PIXELS
 ;; left to right, two columns for letter
 ;; row by row 
 char_a_blue:
  db #00, #00
  db #00, #00
  db #07, #08
  db #00, #0c
  db #07, #0c
  db #0c, #0c
  db #07, #06
  db #00, #00
 ret
 ;;
 char_a_yellow:
  db #00, #00
  db #00, #00
  db #70, #80
  db #00, #c0
  db #70, #c0
  db #c0, #c0
  db #70, #60
  db #00, #00
 ret
 ;;
 hyphen_red:
  db #00, #00
  db #00, #00
  db #00, #00
  db #ff, #ff
  db #ff, #ff
  db #00, #00
  db #00, #00
  db #00, #00
 ret

Answer 1

Maybe start with the Text Output routines in the Amstrad firmware. See 'The Text VDU' section of http://www.cantrell.org.uk/david/tech/cpc/cpc-firmware/firmware.pdf for more details.

TXT SET PEN will set the text colour, and TXT OUTPUT will write each character. Alternatively, you can just use control codes, so output the character 15 (0xF) followed by the pen number (0 to 15) will write following characters in the pen colour defined in the current palette.

Here's an example from https://www.chibiakumas.com/z80/platform.php#LessonP1

Answer 2

It's a simple solution, but the firmware information was not clear to me, just now I got it:

org &4000
run &4000
ld a,2     ; Pen number 2
call &bb90 ; TXT SET PEN (light blue)
ld A,65    ; 65 is ASCII FOR 'A'
call &BB5A ; TXT OUTPUT
jp $