Difference between revisions of "Z80"

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* AF = AL + Flags
 
* AF = AL + Flags
* HL = Can be seen as BX (H=BH,L=BL) or SI in a (HL) setting, like BX also used for adressing.
+
* 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  
 
* 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
 
* DE = Can be seen as DX (D=DH,E=DL) or DI in a (DE) setting
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* IY = 16 bit Index Register Y, can also be accessed with IYH,IYL
 
* IY = 16 bit Index Register Y, can also be accessed with IYH,IYL
  
For each register, there also exists a shadow register that can be swapped out by using the EX instruction.
+
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.  
 
Note: For a lot of operations, you can only use the A(8bit) and HL(16bit) registers.  
The Sjasmplus assembler doesn't really do proper syntax checking for this so beware.
+
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 ===
 
=== Instructions ===
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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.
 
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.
  
== ZX Spectrum  ==
+
Also, here is a compact 'cheat sheet' with some basics for various Z80 systems:
The ZX Spectrum consists of a Z80A @ 3.5 MHz CPU with either 16k, 48k or 128K of RAM.
+
https://www.chibiakumas.com/z80/CheatSheet.pdf
  
=== Setting up ===
+
== Z80 Plaforms ==
Setting up your development platform for the ZX Spectrum is quite easy, first get the following tools:
+
*'''[[ZX Spectrum]]''' - ZX Spectrum Sizecoding information
 
+
*'''[[Amstrad CPC]]''' - Amstrad CPC Sizecoding information
* 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/
 
* 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.
 
 
 
=== 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)
 
 
 
 
 
==== 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
 
 
 
 
 
==== Border Color ====
 
You can set the border color to any of the 8 colors with:
 
 
 
<syntaxhighlight lang="z80">
 
out (254),color
 
</syntaxhighlight>
 
 
 
==== Getting something on screen ====
 
To be added soon.
 
 
 
=== 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 ====
 
To be added soon.
 
 
 
==== Make some noise - AY ====
 
You can access the AY soundchip be 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
 
 
 
=== Additional Resources ===
 
I found resources on ZX Spectrum sizecoding to be sparse.
 
* All kinds of Z80 Information http://www.z80.info/index.htm
 
* Blogpost on ZX Spectrum coding from a X86 coder's perspectove on superogue's sizecdoing blog (soon)
 
* 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
 
 
 
== Amstrad CPC ==
 
The Amstrad consists of a Z80A @ 3.5 MHz CPU
 
 
 
=== Setting up ===
 
Setting up..
 
 
 
* Assembler: -
 
* Emulator(s): -
 
 
 
=== Video Display ===
 
No information yet
 
 
 
=== Sound ===
 
No information yet
 
 
 
=== Additional Resources ===
 
No information yet
 

Latest revision as of 10:41, 8 April 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

Z80 Plaforms