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