Z80DisAssembler

The Z80 CPU was widely used in the 80s in many home computer. Even today it is often used as a cheap embedded CPU. If you need more information can get one of the following books:

Z80 Disassembler

I created this small disassembler for a Z80 cpu at one afternoon. It is a commandline tool. The size of the ROM and entry points have to be coded directly in the sourcecode.

Every ANSI C++ compiler should compile this program. It only uses some ANSI C functions (look into main()). Current program versions can be compiled successfully with gcc and clang w/o warnings.

The program has two parts:

• Analyze the code. The disassembler tries to analyze what part of the binary data is program code and what part is data. It start with all hardware vectors of the Z80 (RST opcodes, NMI) and parses all jumps via a recursive analyze via ParseOpcode(). Every opcode is marked in an array (OpcodesFlags). There are some exceptions, the parser can't recognize:
  • self modifying code. A ROM shouldn't contain such code.
  • calculated branches with JP (IY), JP (IX) or JP (HL). The parser can't recognize them, either.
  • Jumptables. These are quite common in a ROM. Only solution: disassemble the program and look into the code. If you found a jumptable - like on my Futura aquarium computer - insert some more calls of ParseOpcodes().
  • Unused code. Code that is never called by anybody, could not be found. Make sure that the code is not called via a jump table!
• Disassembly of the code. With the help of the OpcodesFlags table the disassembler now creates the output. This subroutine is quite long. It disassembles one opcode at a specific address in ROM into a buffer. It is coded directly from a list of Z80 opcodes, so the handling of IX and IY could be optimized quite a lot.

The subroutine OpcodeLen() returns the size of one opcode in bytes. It is called while parsing and while disassembling.

The disassembler recognizes some hidden opcodes.

If a routine wanted an "address" to the Z80 code, it is in fact an offset to the array of code. No pointers! Longs are not necessary for a Z80, because the standard Z80 only supports 64k.

This program is freeware. It is not allowed to be used as a base for a commercial product!

Z80 Assembler

I created the assembler for the Z80 a few days later to compile the changes code from the disassembler into an EPROM image and build a new firmware for my aquarium computer. I needed almost two days for the assembler, this means: commandline only... If you want to change the filename of the sourcefile, you have to change main().

This small assembler has some nice gadgets: it is a quite fast tokenizing single-pass assembler with backpatching. It knows all official Z80 opcodes and some undocumented opcodes (mainly with IX and IY). The Z80 syntax is documented in the Zilog documentation.

The assembler allows mathematical expressions in operands: +, -, *, /, % (modulo), & (and), | (or), ! (not), ^ (xor), << (shift left) and >> (shift right). Brackets are also available. The expression parser is located in z80_calc.c. Numbers can be postpended by a D, H or B for decimal, hexadecimal and binary numbers. Numbers prepended by a $ are recognized as hex.

The assembler also knows the most commend pseudo opcodes (look into the sourcefile 'z80_tokenize.cp'):

• ; This line is a comment.
• IF Start the conditional expression. If false, the following sourcecode will be skipped (until ELSE or ENDIF).
• ENDIF End of the condition expression.
• ELSE Include the following code, when the expression on IF was false.
• END End of the sourcecode. The assembler stops here. Optional.
• ORG Set the PC in the 64k address space. E.g. to generate code for address $2000.
• PRINT Print the following text on the console. Great for testing the assembler.
• EQU or = Set a variable.
• DEFB or DB Put a byte at the current address
• DEFW or DW Put a word at the current address (little endian!)
• DEFM or DM Put a string or several bytes seperated with a ',' in the memory, starting at the current address.
• DEFS or DS Set the current address n bytes ahead. Defines space for global variables that have no given value.

The Sourcecode

• z80_assembler.cpp
• z80_assembler.h
• z80_calc.cpp
• z80_compile.cpp
• z80_disassembler.cpp
• z80_tokenize.cpp
• kk_ihex_read.c
• kk_ihex_read.h
• kk_ihex_write.c
• kk_ihex_write.h
• kk_ihex.h