ugBASIC User Manual

   WAIT VBL [raster line]

The WAIT VBL command pauses program execution until a “vertical blank” is encountered. This is a signal that is triggered at each screen refresh, which usually occurs at 50 Hz in PAL standard and 60 Hz in NTSC standard.

Some video chipsets also allow you to specify a specific raster line, so execution will continue when that specific line is reached. If the chipset does not allow this, this constraint will be ignored, while still respecting the arrival of a vertical blank.

  WAIT VBL 100

 WtVb

• Commodore 128 (Zilog Z80)
• Commodore 128 (MOS 8502)
• Commodore 64
• Commodore VIC-20
• Atari (400/800)
• Atari XL/XE
• Commodore 64+REU
• Commodore PLUS/4
• Olivetti Prodest PC128
• Amstrad CPC 664
• TRS-80 Color Computer 3
• TRS-80 Color Computer

If you have encountered a problem using this command, if you think there is a bug or the explanation is unclear, please open an issue for this keyword on GitHub. Thank you!