**Right panel**
Select A, F, B, C, D, E, H, L, SP, or PC, enter a hexadecimal value, and press Enter. 8-bit registers accept two digits; SP and PC accept four. The ± buttons change the value by one.
**Structural diagram**
Click an editable value to open its inline editor. Enter applies, Esc cancels, and Tab / Shift+Tab move to an adjacent field. Arrow keys move within register and multiplexer groups.
All manual changes are range-checked and recorded by Undo/Redo. Editing F preserves the required PSW layout: bit 1 is 1 and bits 3 and 5 are 0.