The BBC and Master Computer Public Domain Library

BD37 Output ASCII characeter or BASIC Token to screen

Submitted by Steve Fewell

Routine:PrintToken
Name: Output ASCII characeter or BASIC Token to screen
Starting Address: &BD37
Entry criteria: A contains the ASCII value to output to the screen.

Description:

Store A in location &37.
If A is less then #&80 then the ASCII character will be output via the &BD94 routine.

&BD94 outputs the character with correct handling of the following:

* The COUNT variable

* New line when COUNT exceeds the WIDTH value

* Redirection of output (to memory) when *EDIT-mode is active

* New line when character to output is &0D ('<cr>')

Otherwise, a BASIC token is been specified by the ASCII character, so output the BASIC Keyword (in ASCII text) as follows:

*1) Set pointer &38-&39 to point to address &8456 -> which is the address of the start of the Token table

*2) Save Y (the current program/command line position) to the Stack

*3) Set Y to 0 (to point to the start of the next Keyword in the &38-&39 token table list.

*4) Load the next character (of the token) from the Token Table (pointed to by (&38,&39) + Y)

*5) Skip all ASCII characters (less then #&80) [incrementing Y for each character skipped]
     Now, the character is the token number that represents the BASIC Keyword specified by the skipped characters

*6) Compare the character against the token we want to output (stored in location &37)
     If the token (character) is equal to &37 then output the Keyword text as follows [&BD5E]:
          * Reset Y to 0 (the start of the ASCII Text Keyword)
          * Load the next character of the Keyword from (&38-&39) + Y.
          * If the character is negative (the token number) then goto Step 9 to exit (as token is now printed).
          * Otherwise, call routine &BD94 to output the ASCII character to the screen.
          * Increment Y (to point to the next character of the BASIC Keyword)
          * If Y is not 0 (less than 255 characters have been printed) then jump back to load the next character of the Keyword
          * Jump to step 9 to exit.

*7) Set the token table pointer (&38,&39) to point to the position after the Token Number (i.e. Add Y + 1 to the pointer).

*8) Jump back to Step 3 to check the next BASIC Keyword in the Token Table list

*9) Retrieve Y from the Stack and exit

Disassembly for the Output ASCII characeter or BASIC Token to screen routine