Scrolls the entire display buffer (or area specified within the display buffer) down.
There had been reports on the community that this function was not implemented on the OS/2 4.5 Toolkit. 
VioScrollDown (TopRow, LeftCol, BotRow, RightCol, Lines, Cell, VioHandle)
- TopRow (ULONG) - input
- Top row to be scrolled.
- LeftCol (ULONG) - input
- Left column to be scrolled.
- BotRow (ULONG) - input
- Bottom row to be scrolled.
- RightCol (ULONG) - input
- Right column to be scrolled.
- Lines (ULONG) - input
- Number of lines.
- Number of lines to be inserted at the top of the screen area being scrolled. If 0 is specified, no lines are scrolled.
- Cell (PBYTE) - input
- Cell to be written.
- Address of the character-attribute pair (2 or 4 bytes) used as a fill character on inserted lines.
- VioHandle (HVIO) - input
- Vio presentation-space handle.
- This must be 0, unless the caller is a Presentation Manager application; in this case, it must be the value returned by VioCreatePS.
rc (APIRET) - returns
VioScrollDown returns one of the following values:
- 0 NO_ERROR
- 355 ERROR_VIO_MODE
- 358 ERROR_VIO_ROW
- 359 ERROR_VIO_COL
- 421 ERROR_VIO_INVALID_PARMS
- 436 ERROR_VIO_INVALID_HANDLE
TopRow = 0 and LeftCol = 0 identifies the top-left corner of the screen.
If a value greater than the maximum value is specified for TopRow, LeftCol, BotRow, RightCol, or Lines, the maximum value for that parameter is used.
If TopRow and LeftCol = 0, and if BotRow, RightCol, and Lines are greater than the screen lines, the entire screen is filled with the character-attribute pair defined by Cell.