Difference between revisions of "Z80 based CPUs"

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So here is a bit of help to get you started:
 
So here is a bit of help to get you started:
  
=== Z80 for X86 programmers  ===
+
=== Registers ===
Z80 can be seen as the little 8bit brother of X86 chipsets, with many similarities.
+
The Z80 can be seen as the little 8-bit brother of X86 chipsets, with many similarities.
 
If you are coming from a X86 background, this might help you get a bit more grip on the Z80.
 
If you are coming from a X86 background, this might help you get a bit more grip on the Z80.
 +
These are the register pairs of the Z80, as seen from a X86 programmers perspective.
  
=== Registers ===
+
* AF = AL + Flags
These are the register pairs of the Z80, as seen from a X86 programmers perspective.
+
* HL = Can be seen as BX (H=BH,L=BL) or SI in a (HL) setting, like BX also used for addressing.
 +
* BC = Can be seen as CX (B=CH,C=CL), often used for loops
 +
* DE = Can be seen as DX (D=DH,E=DL) or DI in a (DE) setting
 +
* IX = 16 bit Index Register X, can also be accessed with IXH,IXL
 +
* IY = 16 bit Index Register Y, can also be accessed with IYH,IYL
 +
 
 +
For each of the main registers there also exists a shadow register. These cannot be accessed directly, but must be swapped in and out with the main register set. The shadow registers are usually denoted by the ' symbol. They can be swapped with the following commands:
 +
* EX AF,AF' = Swaps AF with AF'
 +
* EXX = Swaps BC, DE and HL with BC', DE' and HL'
 +
There are no shadow registers for the index registers.
  
AF = AL + Flags
+
Note: For a lot of operations, you can only use the A(8bit) and HL(16bit) registers.
BC = Can be seen as CX (B=CH,C=CL), often used for loops
+
The Sjasmplus assembler has extra syntax and fake-instructions support which may produce unexpected results when source contains other than official Zilog syntax (but the parser can be configured to work in more relaxed way allowing more variations in syntax).
DE = Can be seen as DX (D=DH,E=DL) or DI in a (DE) setting
 
HL = Can be seen as BC (H=BH,L=BL) or SI in a (SI) setting, like BX also used for adressing.
 
IX = 16 bit Index Register X, can also be accessed with IXH,IXL
 
IX = 16 bit Index Register Y, can also be accessed with IYH,IYL
 
  
 
=== Instructions ===
 
=== Instructions ===
 
Here is a rough translation for some of the Z80 instructions:
 
Here is a rough translation for some of the Z80 instructions:
  
[code]
+
* BIT = TEST
BIT = TEST
+
* CP = CMP (although the Z80 has many other handy compare functionality)
CP = CMP
+
* DJNZ = LOOP (decreases B and checks not zero)
DJNZ = LOOP (decreass B and checks not zero)
+
* EXE = Exchange all registers with Shadow registers, can be used a bit like PUSHA/POPA
EX = XCHG
+
* EX = XCHG
EXE = Exchange all registers with Shadow registers, can be used a bit like PUSHA/POPA
+
* HALT = HLT
HALT = HLT
+
* JP = JMP
JP = JMP
+
* JR = JMP NEAR (Jump Relative)
JR = JMP NEAR (Jump Relative)
+
* LD = MOV
LD = MOV
+
* LDI = MOVSB  (tmp=(HL),(DE)=tmp, DE++, HL++)
LDI = LODSB
+
* LDIR = REP MOVSB   (tmp=(HL),(DE)=tmp, DE++, HL++, BC--)
LDIR = REP MOVSB
+
 
 +
 
 +
=== Learning Z80 Assembler ===
 +
There are many Z80 tutorials available online, but one i found very simple and clear is at this 1996 styled webpage ;-) 
 +
 
 +
* http://www.z80.info/lesson1.htm
 +
* http://www.z80.info/lesson2.htm
 +
* http://www.z80.info/lesson3.htm
 +
* http://www.z80.info/lesson4.htm
 +
* http://www.z80.info/lesson5.htm
 +
 
 +
There is no proper index-page for this, which is why i linked all the lessons above, but you can continue to the next lesson by clicking at the next lesson at the bottom of the page.
 +
 
 +
Also, here is a compact 'cheat sheet' with some basics for various Z80 systems:
 +
https://www.chibiakumas.com/z80/CheatSheet.pdf
 +
 
  
 
== ZX Spectrum  ==
 
== ZX Spectrum  ==
The ZX Spectrum consists of a Z80A @ 3.5 MHz CPU with either 16k, 48k or 128K of RAM.
+
The ZX Spectrum consists of a Z80A @ 3.5 MHz CPU with either 16k, 48k or 128K of RAM. Most demos are targeted at the Spectrum 128 because it includes more memory, a shadow screen buffer and an AY soundchip. The different models have slightly different timings - this will cause issues if you are doing cycle-exact effects like multi-color.
  
 
=== Setting up ===
 
=== Setting up ===
 
Setting up your development platform for the ZX Spectrum is quite easy, first get the following tools:
 
Setting up your development platform for the ZX Spectrum is quite easy, first get the following tools:
  
* Assembler: SJASMPLUS -This assembler has nice macros for creating Binaries and SNA snapshot files out of the box. You can download it at https://sourceforge.net/projects/sjasmplus/
+
* [https://github.com/z00m128/sjasmplus/releases/latest SjASMPlus (z00m's fork)] - cross-platform open source assembler with nice macros for creating Binaries, TAP, TRD and SNA snapshot files out of the box, embedded Lua scripting and support for similar CPUs (Z80/R800/Z80N/i8080/LR35902).
* Emulator(s): I Found FUSE, UnrealSpeccy and EightyOne to work best for my usecase. Most emulators can read TAP, SNA and TRD files out of the box.
+
* Pasmo - for the .TAP create. Available at : http://pasmo.speccy.org
 +
* Emulator(s): I Found [https://www.zophar.net/sinclair/zx-spin.html ZX Sping], [https://sourceforge.net/projects/fuse-emulator/ FUSE], [https://sourceforge.net/projects/unrealspeccyp/ UnrealSpeccy] and [https://www.aptanet.org/eightyone/ EightyOne] to work best for my usecase. Most emulators can read TAP, SNA and TRD files out of the box.
  
 
=== Start values ===
 
=== Start values ===
Line 50: Line 72:
 
* A = C
 
* A = C
  
=== Video diplay ===
+
=== Video display ===
 
Video display on the ZX Spectrum is mostly CPU based with little hardware features. No hardware sprites, no specific text or video modes, only a 256x192 byte screenbuffer with 1bit pixeldata located at $4000 in memory.  
 
Video display on the ZX Spectrum is mostly CPU based with little hardware features. No hardware sprites, no specific text or video modes, only a 256x192 byte screenbuffer with 1bit pixeldata located at $4000 in memory.  
 
It is ordened a bit strange in 3 sections of 256x64 pixels, then character rows, then subrows.
 
It is ordened a bit strange in 3 sections of 256x64 pixels, then character rows, then subrows.
  
ScreenPosition = (page<<11) + (character row<<8) + (subrow<<5)
+
Address = 010RRLLL RRRCCCCC
  
 +
* where RRRRR is the row number (0..23)
 +
* CCCCC is the column number (0..31)
 +
* LLL is the line number within the cell (0..7)
  
=== Adding Color ===
+
Calculating a screen address from XY coordinates is complicated due to the weird screen layout. In a larger demo you would generate a lookup table - it's usually best to avoid such calculations in small demos, but it can be done in under 30 bytes, eg: http://www.breakintoprogram.co.uk/computers/zx-spectrum/screen-memory-layout
 +
 
 +
==== Adding Color ====
 
The ZX Spectrum has a 32x24 colormap located at $5800 where you can write color information for each 8x8 tile.  
 
The ZX Spectrum has a 32x24 colormap located at $5800 where you can write color information for each 8x8 tile.  
 
It has has 8 colors (INK and PAPER) with 2 brightness settings that can be set like this.
 
It has has 8 colors (INK and PAPER) with 2 brightness settings that can be set like this.
Line 63: Line 90:
 
color = brightness(64) | (PAPER<<3) | INK
 
color = brightness(64) | (PAPER<<3) | INK
  
 +
Because updating pixel memory can be slow, especially when you are grasping for bytes, some of the tiny intros on the zx spectrum prefer to use the colorram for the effect, sometimes in combination with an overlaying pattern.
 +
 +
==== Border Color ====
 
You can set the border color to any of the 8 colors with:
 
You can set the border color to any of the 8 colors with:
  
 
<syntaxhighlight lang="z80">
 
<syntaxhighlight lang="z80">
out (254),color
+
ld a,0 ; bottom three bits of a contain the color
 +
out (254),a
 
</syntaxhighlight>
 
</syntaxhighlight>
  
=== Getting something on screen ===
+
=== Memory Configuration ===
To be added soon.
+
128K separated to 8 pages (16384 bytes size)
 +
Default configuration is:
  
 +
: page 5: $4000-$7fff
 +
: page 2: $8000-$Bfff
 +
: page 0: $C000-$Ffff
 +
 +
There are two screens - page 7 and page 5.
 +
port $7FFD allow to control memory and screens:
 +
: bits 0-2 - page number mapped to memory at $C0000
 +
: bit 3 - Select page 5(0) or page 7(1) to be displayed.
 +
: bit 4 - ROM Select. 0-128K,1-48K
 +
 +
Example of use
 +
<syntaxhighlight lang="z80">
 +
loop: ei
 +
halt
 +
pg: ld a,$17
 +
ld bc,$7ffd
 +
out (c),a
 +
xor $0A
 +
ld (pg+1),a
 +
... do something with $C000-$DB00
 +
jp loop
 +
</syntaxhighlight>
 +
 +
$17 is use 48K, map page 7
 +
After xor $0A we'll get value $1D(use 48K ROM, display screen at page 7 and map page5 at $C000).This is so-called "double buffering".
 +
See also : https://worldofspectrum.org/faq/reference/128kreference.htm
 +
 +
==== Getting something on screen ====
 +
Now to get something on screen, lets fill our colorram with a simple AND pattern, like so:
 +
<syntaxhighlight lang="z80">
 +
ld de,5800h
 +
ld b,24
 +
yloop:
 +
  ld c,32
 +
xloop:
 +
  ld a,c
 +
  and b
 +
  and 7    ; make sure range is 0..7
 +
  ld (de),a
 +
  inc de
 +
  dec c
 +
  jr nz,xloop
 +
djnz yloop
 +
</syntaxhighlight>
 +
 +
==== Using a Backbuffer ====
 +
While the above code will run fine, you might want to consider using a backbuffer for more complex stuff. You can then simply write to another adress define by BACKBUFFER (for example A000) and copy the buffer to colorram like so:
 +
 +
<syntaxhighlight lang="z80">
 +
halt              ; synchronize
 +
ld hl,BACKBUFFER 
 +
ld de,5800h
 +
ld bc,768
 +
ldir
 +
</syntaxhighlight>
 +
 +
Another alternative method is to use the 128's memory paging, which provides a second screen buffer. This buffer is located at a different memeory location, but otherwise it is the same:
 +
<syntaxhighlight lang="z80">
 +
; main loop starts here
 +
ld a,00010111b ; set up memory banks and screen here
 +
mainloop
 +
halt ; sync
 +
xor 00001010b ; flip screens
 +
out ($fd),a
 +
push af
 +
 +
; render code goes here
 +
; screen buffer is location at 0xC000 instead of 0x4000
 +
 +
pop af
 +
jr mainloop
 +
</syntaxhighlight>
 +
 +
==== Overlaying simple graphics ====
 +
If you don't want to use a solid color/tile for.
 +
You could copy a single tile across the screen at startup for some flair.
 +
<syntaxhighlight lang="z80">
 +
  ld a,0x55  ; 01010101 pattern
 +
  ld bc,0x1800
 +
copyloop:
 +
  ld (de),a
 +
  inc de
 +
  dec c
 +
jr nz,copyloop
 +
djnz copyloop
 +
</syntaxhighlight>
 +
 +
Alternatively you could generate a pattern using logic operations or random noise/data.
 +
==== Useful routines ====
 +
 +
<syntaxhighlight lang="z80">
 +
;calculate address of next line,HL=address
 +
down_hl:
 +
INC h
 +
LD A,h
 +
AND 7
 +
RET NZ
 +
LD A,L
 +
ADD A,#20
 +
LD L,A
 +
RET C
 +
LD A,H
 +
SUB 8
 +
LD H,A
 +
RET
 +
</syntaxhighlight>
 +
 +
<syntaxhighlight lang="z80">
 +
;move up at screen, HL=address
 +
up_hl
 +
    LD A,H
 +
    DEC H
 +
    AND 7
 +
    ret nz
 +
    LD A,L
 +
    SUB 32
 +
    LD L,A
 +
    ret c
 +
    LD A,H
 +
    ADD A,8
 +
    LD H,A
 +
ret
 +
</syntaxhighlight>
 +
 +
<syntaxhighlight lang="z80">
 +
;write pixel
 +
CALL  8933 ; C=X(0..255),B=Y(0..175),5C7D=COORDS
 +
</syntaxhighlight>
 +
 +
<syntaxhighlight lang="z80">
 +
;Calculate vertical line screen Address, IN : A=Y coordinate, OUT : HL=address
 +
py2saddr:
 +
        ld l,a
 +
; ld a,l
 +
and $07
 +
ld h,a
 +
ld a,l
 +
and $c0
 +
rra
 +
inc a
 +
rrca
 +
rrca
 +
or h
 +
ld h,a
 +
ld a,l
 +
add a
 +
add a
 +
and $e0
 +
ld l,a
 +
</syntaxhighlight>
 +
 +
<syntaxhighlight lang="z80">
 +
;Calculate Attribute address, IB: reg D=Y,reg E=X, OUT: HL=address, destroys DE
 +
ld l,d
 +
add hl,hl
 +
add hl,hl
 +
ld h,$11
 +
add hl,hl
 +
add hl,hl
 +
add hl,hl
 +
ld d,0
 +
add hl,de
 +
</syntaxhighlight>
 +
 +
or alter version
 +
<syntaxhighlight lang="z80">
 +
;H=Y coordinate,L=X coordinate
 +
ld a,h
 +
rrca
 +
rrca
 +
rrca
 +
push af
 +
and 3
 +
add a,$58
 +
ld h,a
 +
pop af
 +
and %11100000
 +
add a,l
 +
ld l,a
 +
</syntaxhighlight>
 +
 +
calculate Pixel coordinate
 +
<syntaxhighlight lang="z80">
 +
;IN: A=X coordinate,C=L=Y coordinate
 +
;OUT: HL=screen address,A=bit value
 +
call #22B0
 +
</syntaxhighlight>
  
 
=== Sound ===
 
=== Sound ===
Line 77: Line 296:
 
Later models included the AY-3-8910 Soundchip which provides 3 channels of PSG sound.
 
Later models included the AY-3-8910 Soundchip which provides 3 channels of PSG sound.
  
=== Make some noise - Beeper ===
+
==== Make some noise - Beeper ====
To be added soon.
+
Setting/toggling bit 4 of port 254 will enable the beeper speaker.
  
=== Make some noise - AY ===
+
<syntaxhighlight lang="z80">
To be added soon.
+
ld a,$10 ;Bit 4 set
 +
beeploop: xor $10 ;toggle Bit 4
 +
out (254),a
 +
ld b,90 ;wait
 +
djnz $
 +
jp beeploop
 +
</syntaxhighlight>
 +
Note that the bottom three bits of port 254 also set the border color (see above).
 +
 
 +
==== Make some noise - AY ====
 +
You can access the AY soundchip by outputting to the following ports:
 +
 
 +
<syntaxhighlight lang="z80">
 +
ld bc,0xfffd
 +
ld a, ay register number
 +
out (c),a
 +
ld b,0xbf
 +
ld a, data byte
 +
out (c),a
 +
</syntaxhighlight>
 +
 
 +
For more information about the soundchip, check out:
 +
https://www.atarimagazines.com/v4n7/stsound.html
 +
 
 +
=== Small demos with documented source code ===
 +
* Ceci N'est Pas Un Cube by Ate Bit https://www.pouet.net/prod.php?which=29691
 +
* Zxwister by Ate Bit https://www.pouet.net/prod.php?which=44123
 +
* Muse by Ate Bit https://www.pouet.net/prod.php?which=62880
 +
* Starlet Guitarlet by HOOY-PROGRAM https://www.pouet.net/prod.php?which=52553
 +
* Clangers On The Dancefloor by HOOY-PROGRAM https://www.pouet.net/prod.php?which=29696
 +
* Chessington World Of Adventure by HOOY-PROGRAM https://www.pouet.net/prod.php?which=76074
 +
* Roll Me Gently by Joker https://www.pouet.net/prod.php?which=86338
  
 
=== Additional Resources ===
 
=== Additional Resources ===
 
I found resources on ZX Spectrum sizecoding to be sparse.
 
I found resources on ZX Spectrum sizecoding to be sparse.
* Blogpost on ZX Spectrum coding from a X86 coder's perspectove on superogue's sizecdoing blog (soon)
+
* All kinds of Z80 Information http://www.z80.info/index.htm
* 128byte/256 byte zx spectrum productions by goblinish on pouet.net https://www.pouet.net/groups.php?which=11696&order=platform&reverse=1
+
* Another source for good Z80 Information http://z80-heaven.wikidot.com
* 128byte/256 byte zx spectrum productions by gasman on pouet.net https://www.pouet.net/user.php?who=2260&show=credits
+
* Assembler subforum on world of spectrum https://worldofspectrum.org/forums/categories/assembler
 +
* Development subforum on Spectrum Computing https://spectrumcomputing.co.uk/forums/viewforum.php?f=6
 +
* Blogpost on ZX Spectrum coding from a X86 coder's perspective on superogue's sizecdoing blog http://marquee.revival-studios.com/blog/blog_fluxus.html
 +
* 128byte/256 byte zx spectrum productions by goblinish https://www.pouet.net/groups.php?which=11696&order=type
 +
* 128byte/256 byte zx spectrum productions by gasman https://www.pouet.net/groups.php?which=1218&order=type
 +
* Easy to read list of all Z80 instructions (including undocumented ones) with size and timing information https://clrhome.org/table/
 +
* Detailed information on the screen layout http://www.overtakenbyevents.com/lets-talk-about-the-zx-specrum-screen-layout/ http://www.overtakenbyevents.com/lets-talk-about-the-zx-specrum-screen-layout-part-two/ and http://www.overtakenbyevents.com/lets-talk-about-the-zx-specrum-screen-layout-part-three/
 +
 
 +
== Amstrad CPC ==
 +
The Amstrad consists of a Z80A @ 3.5 MHz CPU
 +
 
 +
=== Setting up ===
 +
Setting up:
 +
 
 +
* Assembler: -
 +
** The emulator [http://www.winape.net/ Winape] has an integrated [http://www.winape.net/help/assembler.html assembler]
 +
** cross-platform [https://github.com/z00m128/sjasmplus/releases/latest SjASMPlus] assembler will have support for CPC snapshot and CDT files in next version v1.18.4.
 +
 
 +
* Emulator(s):
 +
** [http://www.winape.net/ Winape] is very accurate and includes an assembler / debugger
 +
** [https://www.cpc-power.com/cpcarchives/index.php?page=articles&num=445 Caprice] gets very regular updates
 +
** [http://cngsoft.no-ip.org/cpcec.htm CPCEC] is very fast
 +
** [https://sourceforge.net/projects/javacpc/ JavaCPC] offers many features
 +
** [https://www.retrovirtualmachine.org/ Retro Virtual Machine] is visually very impressiv
 +
 
 +
=== Video Display ===
 +
No information yet
 +
 
 +
=== Sound ===
 +
No information yet
 +
 
 +
=== Additional Resources ===
 +
* 64 NOPs Amstrad CPC Tech Blog - https://64nops.wordpress.com/

Latest revision as of 18:25, 11 January 2022

Introduction

Wanting to start sizecoding on a Z80 platform in this day and age can be tough.

So here is a bit of help to get you started:

Registers

The Z80 can be seen as the little 8-bit brother of X86 chipsets, with many similarities. If you are coming from a X86 background, this might help you get a bit more grip on the Z80. These are the register pairs of the Z80, as seen from a X86 programmers perspective.

  • AF = AL + Flags
  • HL = Can be seen as BX (H=BH,L=BL) or SI in a (HL) setting, like BX also used for addressing.
  • BC = Can be seen as CX (B=CH,C=CL), often used for loops
  • DE = Can be seen as DX (D=DH,E=DL) or DI in a (DE) setting
  • IX = 16 bit Index Register X, can also be accessed with IXH,IXL
  • IY = 16 bit Index Register Y, can also be accessed with IYH,IYL

For each of the main registers there also exists a shadow register. These cannot be accessed directly, but must be swapped in and out with the main register set. The shadow registers are usually denoted by the ' symbol. They can be swapped with the following commands:

  • EX AF,AF' = Swaps AF with AF'
  • EXX = Swaps BC, DE and HL with BC', DE' and HL'

There are no shadow registers for the index registers.

Note: For a lot of operations, you can only use the A(8bit) and HL(16bit) registers. The Sjasmplus assembler has extra syntax and fake-instructions support which may produce unexpected results when source contains other than official Zilog syntax (but the parser can be configured to work in more relaxed way allowing more variations in syntax).

Instructions

Here is a rough translation for some of the Z80 instructions:

  • BIT = TEST
  • CP = CMP (although the Z80 has many other handy compare functionality)
  • DJNZ = LOOP (decreases B and checks not zero)
  • EXE = Exchange all registers with Shadow registers, can be used a bit like PUSHA/POPA
  • EX = XCHG
  • HALT = HLT
  • JP = JMP
  • JR = JMP NEAR (Jump Relative)
  • LD = MOV
  • LDI = MOVSB (tmp=(HL),(DE)=tmp, DE++, HL++)
  • LDIR = REP MOVSB (tmp=(HL),(DE)=tmp, DE++, HL++, BC--)


Learning Z80 Assembler

There are many Z80 tutorials available online, but one i found very simple and clear is at this 1996 styled webpage ;-)

There is no proper index-page for this, which is why i linked all the lessons above, but you can continue to the next lesson by clicking at the next lesson at the bottom of the page.

Also, here is a compact 'cheat sheet' with some basics for various Z80 systems: https://www.chibiakumas.com/z80/CheatSheet.pdf


ZX Spectrum

The ZX Spectrum consists of a Z80A @ 3.5 MHz CPU with either 16k, 48k or 128K of RAM. Most demos are targeted at the Spectrum 128 because it includes more memory, a shadow screen buffer and an AY soundchip. The different models have slightly different timings - this will cause issues if you are doing cycle-exact effects like multi-color.

Setting up

Setting up your development platform for the ZX Spectrum is quite easy, first get the following tools:

  • SjASMPlus (z00m's fork) - cross-platform open source assembler with nice macros for creating Binaries, TAP, TRD and SNA snapshot files out of the box, embedded Lua scripting and support for similar CPUs (Z80/R800/Z80N/i8080/LR35902).
  • Pasmo - for the .TAP create. Available at : http://pasmo.speccy.org
  • Emulator(s): I Found ZX Sping, FUSE, UnrealSpeccy and EightyOne to work best for my usecase. Most emulators can read TAP, SNA and TRD files out of the box.

Start values

Upon startup (when called from basic), the following values can assumed:

  • The alternate HL register is set to 0x2758
  • BC = start address
  • A = C

Video display

Video display on the ZX Spectrum is mostly CPU based with little hardware features. No hardware sprites, no specific text or video modes, only a 256x192 byte screenbuffer with 1bit pixeldata located at $4000 in memory. It is ordened a bit strange in 3 sections of 256x64 pixels, then character rows, then subrows.

Address = 010RRLLL RRRCCCCC

  • where RRRRR is the row number (0..23)
  • CCCCC is the column number (0..31)
  • LLL is the line number within the cell (0..7)

Calculating a screen address from XY coordinates is complicated due to the weird screen layout. In a larger demo you would generate a lookup table - it's usually best to avoid such calculations in small demos, but it can be done in under 30 bytes, eg: http://www.breakintoprogram.co.uk/computers/zx-spectrum/screen-memory-layout

Adding Color

The ZX Spectrum has a 32x24 colormap located at $5800 where you can write color information for each 8x8 tile. It has has 8 colors (INK and PAPER) with 2 brightness settings that can be set like this.

color = brightness(64) | (PAPER<<3) | INK

Because updating pixel memory can be slow, especially when you are grasping for bytes, some of the tiny intros on the zx spectrum prefer to use the colorram for the effect, sometimes in combination with an overlaying pattern.

Border Color

You can set the border color to any of the 8 colors with:

ld a,0 ; bottom three bits of a contain the color
out (254),a

Memory Configuration

128K separated to 8 pages (16384 bytes size) Default configuration is:

page 5: $4000-$7fff
page 2: $8000-$Bfff
page 0: $C000-$Ffff

There are two screens - page 7 and page 5. port $7FFD allow to control memory and screens:

bits 0-2 - page number mapped to memory at $C0000
bit 3 - Select page 5(0) or page 7(1) to be displayed.
bit 4 - ROM Select. 0-128K,1-48K

Example of use

loop: ei
 halt
pg: ld a,$17
 ld bc,$7ffd
 out (c),a
 xor $0A
 ld (pg+1),a
... do something with $C000-$DB00
 jp loop

$17 is use 48K, map page 7 After xor $0A we'll get value $1D(use 48K ROM, display screen at page 7 and map page5 at $C000).This is so-called "double buffering". See also : https://worldofspectrum.org/faq/reference/128kreference.htm

Getting something on screen

Now to get something on screen, lets fill our colorram with a simple AND pattern, like so:

 ld de,5800h
 ld b,24
yloop:
   ld c,32
xloop:
   ld a,c
   and b
   and 7    ; make sure range is 0..7
   ld (de),a
   inc de
   dec c
   jr nz,xloop
djnz yloop

Using a Backbuffer

While the above code will run fine, you might want to consider using a backbuffer for more complex stuff. You can then simply write to another adress define by BACKBUFFER (for example A000) and copy the buffer to colorram like so:

halt               ; synchronize 
ld hl,BACKBUFFER   
ld de,5800h
ld bc,768
ldir

Another alternative method is to use the 128's memory paging, which provides a second screen buffer. This buffer is located at a different memeory location, but otherwise it is the same:

	; main loop starts here
	ld	a,00010111b	; set up memory banks and screen here
mainloop
	halt			; sync
	xor	00001010b	; flip screens
	out	($fd),a
	push	af

	; render code goes here
	; screen buffer is location at 0xC000 instead of 0x4000

	pop	af
	jr	mainloop

Overlaying simple graphics

If you don't want to use a solid color/tile for. You could copy a single tile across the screen at startup for some flair.

   ld a,0x55   ; 01010101 pattern
   ld bc,0x1800
copyloop:
   ld (de),a
   inc de
   dec c
jr nz,copyloop
djnz copyloop

Alternatively you could generate a pattern using logic operations or random noise/data.

Useful routines

;calculate address of next line,HL=address
down_hl:
 INC h
 LD A,h
 AND 7
 RET NZ
 LD A,L
 ADD A,#20
 LD L,A
 RET C
 LD A,H
 SUB 8
 LD H,A
 RET
;move up at screen, HL=address
up_hl
     LD A,H
     DEC H
     AND 7
     ret nz
     LD A,L
     SUB 32
     LD L,A
     ret c
     LD A,H
     ADD A,8
     LD H,A
 ret
;write pixel
 CALL  8933 ; C=X(0..255),B=Y(0..175),5C7D=COORDS
;Calculate vertical line screen Address, IN : A=Y coordinate, OUT : HL=address
py2saddr:
        ld l,a
;	ld a,l
	and $07
	ld h,a
	ld a,l
	and $c0
	rra
	inc a
	rrca
	rrca
	or h
	ld h,a
	ld a,l
	add a
	add a
	and $e0
	ld l,a
;Calculate Attribute address, IB: reg D=Y,reg E=X, OUT: HL=address, destroys DE
 ld l,d
 add hl,hl
 add hl,hl
 ld h,$11
 add hl,hl
 add hl,hl
 add hl,hl
 ld d,0
 add hl,de

or alter version

;H=Y coordinate,L=X coordinate
	ld a,h
	rrca
	rrca
	rrca
	push af
	and 3
	add a,$58
	ld h,a
	pop af
	and %11100000
	add a,l
	ld l,a

calculate Pixel coordinate

;IN: A=X coordinate,C=L=Y coordinate
;OUT: HL=screen address,A=bit value
call #22B0

Sound

The original Spectrum has only a 1 bit sound capability (BEEP) through its internal speaker. Later models included the AY-3-8910 Soundchip which provides 3 channels of PSG sound.

Make some noise - Beeper

Setting/toggling bit 4 of port 254 will enable the beeper speaker.

		ld a,$10	;Bit 4 set
beeploop:	xor $10		;toggle Bit 4
		out (254),a
		ld b,90		;wait
		djnz $
		jp beeploop

Note that the bottom three bits of port 254 also set the border color (see above).

Make some noise - AY

You can access the AY soundchip by outputting to the following ports:

ld bc,0xfffd
ld a, ay register number
out (c),a
ld b,0xbf	
ld a, data byte
out (c),a

For more information about the soundchip, check out: https://www.atarimagazines.com/v4n7/stsound.html

Small demos with documented source code

Additional Resources

I found resources on ZX Spectrum sizecoding to be sparse.

Amstrad CPC

The Amstrad consists of a Z80A @ 3.5 MHz CPU

Setting up

Setting up:

  • Assembler: -
    • The emulator Winape has an integrated assembler
    • cross-platform SjASMPlus assembler will have support for CPC snapshot and CDT files in next version v1.18.4.

Video Display

No information yet

Sound

No information yet

Additional Resources