write_command.md

W: Write Memory Command

Purpose

Interactively write hex bytes to memory starting at a specified address.

Activation

• Command letter: W
• Format: W:address

Input Requirements

Start Address

• address: 4-digit hexadecimal address (0000-FFFF)
• No range required - single starting address only

Interactive Mode

After issuing the command, the monitor enters write mode:

1. Displays current address and existing byte value
2. Waits for hex byte input or control keys
3. Advances to next address after each write
4. Continues until ESC is pressed

Input Format in Write Mode

• Enter 2-digit hex bytes (00-FF)
• Press ENTER to confirm and advance to next address
• Press ESC to exit write mode
• Press . (dot) to recall last command

Display Format

XXXX: YY _

Where:

• XXXX = current address in hex
• YY = existing byte value at address
• _ = cursor waiting for input

Examples

• W:8000 - Start writing at $8000
• Input: A9 + ENTER - Write $A9 to current address, advance
• Input: 20 + ENTER - Write $20 to next address, advance
• Input: ESC - Exit write mode

Success Behavior

• Each successful write advances to the next address
• No explicit success message - advancing indicates success
• Returns to command mode when ESC pressed

Error Messages

• ?ERROR - Invalid syntax or hex address
• ?VALUE - Invalid hex byte entered during write mode

Notes

• Write mode preserves command in history for dot recall
• Can write to any address in memory map
• No range checking - single bytes only
• Displays old value before overwriting