The BBC and Master Computer Public Domain Library

980D VDU

Submitted by Steve Fewell

Description:

[&980D] Get the next non-space character (from BASIC Text Pointer A) after the 'VDU' keyword.
[&9810] If end of VDU statement found (i.e. the character is ':', '<cr>' [carriage-return] or 'ELSE-token') then jump to
&9000 to execute the next command line or program statement.

If not end of statement found, then decrement BASIC Text pointer A Offset (&0A), and call routine &926F to get the
result of the expression at BASIC Text Pointer A position and convert the result to Integer (or issue 'Syntax Error' if
a String value was found).

Call routine &9840 to output the ASCII Code in the IWA LSB byte (location &2A) to the screen.

Get the next non-space character. If the character is ',' [comma] then jump back to &980D to check for any further VDU
codes.
If the character is ';' [semi-colon] then [&9808] Output the ASCII code in location &2B (the MSB byte of the 16-bit
value in the IWA) to the screen, and then continue with &980D (to check for further VDU codes to output).
If the character is '|' [vertical-bar] then output 9 ASCII-0 [Nul] bytes to complete any pending VDU statements and then
jump back to &980D to check for further VDU codes to output.

If the character isn't ',', ';' or '|' then jump back to &9810 to check for end of statement and output further
VDU codes (if end of statement isn't found).
This enables VDU calls such as 'W%=67: VDU 65W%66|68&66(69)' to be accepted and display the result: 'ACBDfE'!
And additionally allows for spaces to be used instead of commas.

Disassembly for the VDU routine