VDU 22

From BeebWiki

Selects a display MODE.

VDU 22

Syntax	VDU 22,<numeric>
Character stream (hex)	16 <mode>
Description	Changes the display to MODE <mode>

Description

VDU 22,n changes the display to MODE n. For a list of display modes, see MODE.

• The start of display memory is moved, but the current language is not informed.
• The CRTC, video ULA and address translation latches are reprogrammed, taking into account the *TV setting.
• Changing to a graphics mode, the actions of VDU 20 are performed:
  • The video ULA's palette is reset for the new mode.
  • The text and graphics foreground colours are set to white.
  • The text and graphics background colours are set to black.
  • The foreground and background graphics paint modes are set to 'overwrite'.
• The text and graphics windows are reset to fill the whole display.
• The text and graphics cursors are uncoupled.
• The text window (the whole screen) is cleared.
• Paged mode is turned off.
• The text cursor is made visible and returned home.

Since the display memory may 'explode' without the current language being informed, VDU 22,n can corrupt user memory in the I/O processor. Mode changes must therefore be made through the language (for instance in BASIC, by the statement MODE n.)

When user memory is separate from display memory (that is, when *SHADOW mode, a Tube coprocessor or the Archimedes is in use) then mode changes can be made by either method.

The start of display memory for a given MODE can be found without changing to that MODE, with OSBYTE &85.

-- beardo 20:52, 10 November 2007 (UTC)