Applesoft: Internals--TXTPTR routines (2 of 2)



CHRGET          00B1



CHRGET increments TXTPTR.  Use CHRGOT to get the character.  TXTPTR now

points at:



CHRGOT          00B7



CHRGOT loads A from TXTPTR and sets certain 6502 status flags.  X and Y are

not changed.  On exit:



A = the character currently pointed at by TXTPTR

Z is set if A is ":" or eol ($3A or $00)

C is clear if A is an ASCII number("0" to "9").



LINGET          DA0C



LINGET read a line number (integer 0 to 63999) from TXTPTR into LINNUM.

LINGET assumes the 6502 registers and A have been set up by the JSR to CHRGET

that fetched the first digit.  LINGET normally exits through CHARGET, which

fetches the character after the last digit.  When the number is greater than

63999, LINGET exits via SYNTAX ERROR.  LINNUM is zero when there is no number

at TXTPTR.



GTBYTC          E6F5



GTBYTC causes JSR to CHRGET to gobble a character, then evaluates the formula

at TXTPTR, and then it returns a single byte integer in X and FACLO.  On

entry TXTPTR points to the first character of the formula.  GTBYTC normally

exits through CHRGET.  If FAC is greater than 255 or less than 0, it exits

through ILLEGAL QUANTITY ERROR.



GETBYT          E6F8



GETBYT evaluates the formula at TXTPTR besides returning a single byte

integer in X and FACLO.  On entry, TXTPTR points to the first character of

the formula.  GETBYT normally exits through CHRGET.  When FAC is greater than

255 or less than 0, it exits through ILLEGAL QUANTITY ERROR.



PLOTFNS         F1EC



PLOTFNS gets two LORES plotting coordinates separated by a comma from TXTPTR

(0-47,0-47).  TXTPTR when entered, points to the first number of the formula.

PLOTFNS puts the first number in FIRST and the second number in H2 and V2.



HFNS            F6B9



HGNS gets HIRES plotting coordinates (0-279,0-191) from TXTPTR.  TXTPTR

points to the first character of the formula for the first number upon entry.

HFNS leaves the 6502 registers set up for HPOSN.  When exiting:



A = vertical coordinate

X = lsb of horizontal coordinate

Y = msb of vertical coordinate





Apple Tech Notes





Keywords:  <None>



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This information is from the Apple Technical Information Library.



ArticleID: TECHINFO-0000073



19960724 15:55:27.00

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