charset224
Description of the page content
A 8-bit charset printing mode for ZX BASIC.
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Description
charset224 is an alternative printing mode for the ZX BASIC language.
charset224 makes it possible to use a standard 8-bit charset instead of the legacy ZX Spectrum charset. A Latin1 charset is included, though not complete yet.
Usage
I assume you are acquainted with ZX BASIC and GNU/Linux:
In order to use charset224 the print.modified_for_charset224.z80s library must be used instead of the original ZX BASIC's library-asm/print.asm:
Rename print.asm to print_ORIGINAL.fs and copy print_charset224.z80s to library-asm/. Then create a symbolic link with the original name print.asm pointing print_charset224.z80s.
Now you can include charset224.zxbas in your own programs. See the source of the demo.
Screenshots
The demo:
Source code
' charset224.zxbas
' An addon for ZX BASIC (http://zxbasic.net)
' Version A-00-20140511
' This file is part of charset224
' (http://programandala.net/en.program.charset224.html)
' Copyright (C) 2014 Marcos Cruz (programandala.net)
' This program is free software; you can redistribute it and/or modify
' it under the terms of the GNU General Public License as published by
' the Free Software Foundation; either version 3 of the License, or
' (at your option) any later version.
'
' This program is distributed in the hope that it will be useful, but
' WITHOUT ANY WARRANTY; without even the implied warranty of
' MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
' General Public License for more details.
'
' You should have received a copy of the GNU General Public License
' along with this program; if not, see <http://gnu.org/licenses>.
' --------------------------------------------------------------
' Description
' This ZX BASIC file provides a sub called 'charset224'. It activates
' or deactivates a new printing mode. In the new mode, all 224 chars
' from 0x20 to 0xFF are printed as ordinary chars from the standard
' charset pointed by the CHARS system variable (no UDG, no block
' graphics, no tokens). Of course in order to use the new mode a
' proper 224-char font has to be in memory and CHARS has to be changed
' accordingly.
' The objective is to use a standard 8-bit character set (e.g. Latin
' 1) in ZX BASIC programs. This is very useful for programs in other
' languages than English, especially for programs that need a lot of
' text (text adventures or certain applications): No special notation
' or tricks are required in order to use standard non-ASCII chars into
' the texts the program will show at run-time.
' A 224-char font ocuppies 1792 bytes, and probably most of the chars
' will not be required by most programs, but the space of the unused
' chars can be used for graphics, data or even Z80 code.
' --------------------------------------------------------------
' Idea for an improved version
' A new printing mode to use the new font only for chars greater than
' 0x7E. This option would save 752 bytes. This mode would be useful
' for large programs that do not need a whole 255-bit new font design,
' but just need to add the missing standard non-ASCII chars to the
' ordinary ZX Spectrum font.
' --------------------------------------------------------------
' History
' 2014-05-06: First simple version. The parameter of the sub is the
' jump opcode required to hack the original <library-asm/print.asm>
' with. Two lines of code have to be previously and permanently
' modified in <library-asm/print.asm>.
' 2014-05-11: The code was rewritten and improved with a different
' approach: The original <library-asm/print.asm> has not to be
' previously modified, only a new label has to be added to it. All
' required changes are done by the sub. Its parameter is just a flag.
' The program is renamed.
' --------------------------------------------------------------
#ifndef __LIBRARY_CHARSET224__
' Avoid recursive / multiple inclusion
#define __LIBRARY_CHARSET224__
sub fastcall charset224(flag as ubyte)
' This sub modifies the Z80 code of ZX BASIC's
' <library-asm/print.asm>, in order to change its behaviour.
' If flag=0
' the legacy ZX Spectrum charset printing mode is set
' (ordinary chars, UDG and block graphics are managed differently).
' This is the original behaviour of the printing routine.
' If flag<>0
' the modern 8-bit charset printing mode is set
' (all chars 20h-FFh are ordinary).
asm
proc
ld hl,JUMP_IF_GREATER_THAN_80H ; address of the jump to be modified
and a
jr nz,MODIFY_THE_ORIGINAL_CODE
local RESTORE_THE_ORIGINAL_CODE
RESTORE_THE_ORIGINAL_CODE:
; Set the legacy ZX Spectrum charset printing mode
ld (HL),218 ; = 0xDA = Z80 'JP C'
call READY
; original code
add a, a ; 1 byte
ld l, a ; 1 byte
ld h, 0 ; 2 bytes
local MODIFY_THE_ORIGINAL_CODE
MODIFY_THE_ORIGINAL_CODE:
; Set the modern 8-bit charset printing mode
ld (HL),195 ; = 0xC3 = Z80 'JP'
call READY
; code to overwrite the original version with
ld l, a ; 1 byte
ld h, 0 ; 2 bytes
add hl,hl ; 1 byte
local READY
READY:
pop hl ; get the source address from the stack
ld de,__PRGRAPH0 ; destination address
ld bc,4 ; count
ldir
endp
end asm
end sub
#endif