Applesoft: Internals--Introduction (1 of 2)



The following six notes, first published in The Apple Orchard (March 1980)

are written for experienced 6502 machine language programmers who wish to use

the Applesoft ROM subroutines. The addresses given are for an Apple II+

with an Applesoft firmware card, or Applesoft loaded into a Language Card.

Consult your Applesoft Reference manual for more information.



Take special note of CHRGET, the heart of Applesoft.  When Applesoft wants

the next character of an instruction, it points TXTPTR at the program or

input buffer, and JSRs to CHRGET.  TXTPTR is temporarily set to the last used

DATA statement when Applesoft READS DATA.



ABBREVIATIONS



 msb:   most significant bit or byte

 lsb:   least significant bit or byte

 eol:   end of line token ($00)



 A:  the 6502 accumulator

 X:  the 6502 X register

 Y:  the 6502 Y register

 Z:  the zero flag of the 6502 status register

 C:  the carry flag of the 6502 status register



 A,X is a 16 bit number where A has the msb and X the lsb.



 (Y,A) is the number or string whose address is in Y and A, with the msb in

       Y and lsb in A.



 FAC    the floating point accumulator

 ARG    the ARGument register





Apple Tech Notes





Keywords:  <None>



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This information is from the Apple Technical Information Library.



ArticleID: TECHINFO-0000072



19960724 15:55:27.00

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