Arduino Z80 Monitor

• Uses Arduino Nano/Uno, two 74HC573 latches, parallel SRAM, and Z80 CPU
• Built-in assembler, disassembler, and memory monitor
• Import and export memory in IHX format

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• Coding and breadboarding tutorial

Assembling the circuit

Building the software

Use the PlatformIO plugin for VSCode.

Open the project folder with VSCode, select the environment for your board (uno, nano, oldnano), and click Upload.

The core library is required and PlatformIO will download this into the .pio folder.

Distributed under the MIT license

Using the built-in commands

After building and uploading the program to the Arduino, connect a serial monitor such as the one included with PlatformIO. A > should appear as a prompt for input. For commands taking integer parameters, values may be specified as decimal 255, hex $FF, octal &377, or binary %11111111. The following commands are available:

>baud [rate]

The baud rate defaults to 9600, but can be changed at runtime. Type ctrl-t b [rate] in the PlatformIO terminal to match the changed baud rate. Setting the baud rate too high can cause IHX import to fail if it exceeds the EEPROM page write timing. Tested with 115200 and found to be within a safe margin.

Assembler commands

TODO

Memory monitor commands

>hex [base] [size]

Prints a hex dump of ROM data from base to base + size - 1.

>set [base] "string pattern"

Writes ASCII data to memory starting at base. No null terminator is written.

>set [base] "string pattern" 0

Writes ASCII data followed by a null terminator (or any other byte).

>set [base] $41 255 %01000001 'A' "strings too"

Writes byte or ASCII data sequentially to memory starting at base.

>fill [base] [size] [pattern]

Repeats one-byte pattern in memory from base to base + size - 1.

>move [source] [size] [dest]

Copies memory from [source...source + size - 1] to [dest...dest + size - 1]. Destination may overlap with source.

Transferring data in IHX format

Data is transferred in plain text Intel HEX format. Use the bin2ihx script to convert from a binary file or the ihx2bin script to do the reverse.

The plain text data may be copy/pasted into the host terminal or uploaded with a special terminal command. The PlatformIO terminal supports uploading with the ctrl-t ctrl-u escape sequence.

>import

All input following the command will be parsed as Intel HEX and written to memory.

>verify

All input following the command will be parsed as Intel HEX and validated against values read from memory. Prints "PASS" on success. Prints "FAIL" and marks differences with '*' otherwise.

>export [base] [size]

Prints memory from base to base + size - 1 in Intel HEX format.

Example Z80 programs

Add two bytes

Add byte at $100 to byte at $101 and store result at $102

LD HL,$0100
LD A,(HL)
INC HL
ADD A,(HL)
INC HL
LD (HL),A
HALT

Copy-paste to import machine code:

import
:090000002100017E23862377769E
:00000001FF
set $100 $12 $34
run
hex $100

Prints 0100 12 34 46 ...

Rot13 string cypher

Equivalent C code

for (char *ptr = 0x100; *ptr != 0; ++ptr) {
  if (*ptr > 'z') {
    continue;
  } else if (*ptr >= 'n') {
    *ptr -= 13;
  } else if (*ptr >= 'a') {
    *ptr += 13;
  } else if (*ptr > 'Z') {
    continue;
  } else if (*ptr >= 'N') {
    *ptr -= 13;
  } else if (*ptr >= 'A') {
    *ptr += 13;
  }
}

Z80 assembly listing

 // for (char *ptr = 0x100; ...; ...)
 LD HL,$FF // following INC makes $100
next:
 // for (...; ...; ++ptr)
 INC HL
 // for (...; *ptr != 0; ...)
 LD A,(HL)
 CP A,0
 JR NZ,body
 HALT
body:
 // if ('z' < *ptr) continue;
 LD A,'z'
 CP A,(HL)
 JR C,next
 // else if (*ptr >= 'n') *ptr -= 13;
 LD A,(HL)
 CP A,'n'
 JR NC,sub13
 // else if (*ptr >= 'a') *ptr += 13;
 CP A,'a'
 JR NC,add13
 // else if ('Z' < *ptr) continue;
 LD A,'Z'
 CP A,(HL)
 JR C,next
 // else if (*ptr >= 'N') *ptr -= 13;
 LD A,(HL)
 CP A,'N'
 JR NC,sub13
 // else if (*ptr >= 'A') *ptr += 13;
 CP A,'A'
 JR C,next
add13:
 ADD A,13
 LD (HL),A
 JR next
sub13:
 SUB A,13
 LD (HL),A
 JR next

Copy-paste to import machine code and decipher message:

import
:2000000021FF00237EFE002001763E7ABE38F47EFE6E3017FE61300E3E5ABE38E67EFE4EDC
:100020003009FE4138DDC60D7718D8D60D7718D3C4
:00000001FF
set $100 "Lbh'er njrfbzr!" 0
run
hex $100

Copy-paste to disassemble imported machine code:

label next $0003
label body $000A
label add13 $0026
label sub13 $002B
dasm 0 $30