Z80 Sudoku — Register Conventions

Defined to prevent accidental clobbering and to support modular routines.

Primary Roles

• HL — Primary board pointer (cell iterator)• DE — Secondary scan pointer (row/column/box traversal)• BC — Loop counter or candidate bit mask• A — Accumulator for mask construction and comparisons• IX — Pointer to current backtracking frame• SP — Structured backtracking frame storage

Design Principle

All routines should document clobbered registers explicitly.Candidate-builder and validation routines must preserve IX and SP.