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Written By Julian Randell


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Keyword Extension

Julian Randell, Thurmaston, Leicester

When I first saw the Electron, I was interested in the use of the function key - func - as a means of obtaining Basic commands. I therefore decided to implement this idea on my BBC.

Listing 1 is the completed program which can be assembled and then used as a standalone machine-code program. The actual machine-code only takes up two pages of valuable user memory - 512 bytes. Before program entry can begin you must first type:

MODE 7:PAGE = &3000

and then type NEW. Then listing 1 can be typed in; comments and remarks can be left out of course. Then the Basic program should be saved as:

SAVE "KEYWORDS"

This operation is imperative, as the program alters operating system entry points and uses interrupts. Hence it will completely lock up the machine if there is a typing error.

Run the program and if all is well the program will report its Execution address. This should then be called. The computer should reset by itself with the message:

Keyword extension (C) J.P.R.

If this does not happen, reload from tape and check the program through. The program is then used by pressing Tab, released it and pressing the required key as below:

X - MOVE I - INPUT R - RUN A - AUTO J - SAVE S - STEP
B - DEF K - CHAIN T - THEN C - COLOUR L - LIST U - UNTIL
D - DRAW M - MODE V - VDU E - ELSE N - NEXT W - RESTORE
F - FOR O - OLD X - PROC G - GOTO P - PRINT Y - REPEAT
H - LOAD Q - LOCAL Z - END  

I use the program quite often and have stuck these keywords to the front of the respective keys on the keyboard. Finally, to save the program as machine-code only, for users without a disc drive, type:

*SAVE "KEY.M.C" E00 1FF E7C

The program can be easily run at different addresses by altering the value of MEM in line 60. This must not be set to below &E00. For example, for disc users, type:

60 MEM = &1900

To save as machine code, return the program and then type:

*SAVE "KEY.M.C" 1900 1AFF 197C

PAGE will be set to &200 above the base address on Break or Ctrl-Break.