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Initialize to read a string


 6502  On entry: On exit:
Z undefined 0=String is non-empty or quoted
1=String is empty and unquoted
C 0=String terminates at second ", otherwise at first CR or space
1=String terminates at second "</tt">, otherwise at first CR
A undefined First character of string; =&0D if string empty and unquoted
Y Offset to start scan Offset of first character of string
 ?&F2 LSB of start of array preserved
 ?&F3 MSB of start of array preserved

Prepares GSREAD to read a string from a character array. The string may be enclosed in double quotes (<tt>") in which case spaces in the string are preserved. The string may also contain control codes and high-order characters encoded with an escape sequence.

GSINIT starts at the position given by (?&F2,?&F3)+Y and scans forward, incrementing Y until a character other than space or CR is found.

If the string begins with " then &22 is returned in A and (?&F2,?&F3)+Y points to the character after the ". The carry flag input to GSINIT has no effect; GSREAD will return characters until the closing " is reached. CR encountered before the closing " causes error &FD, Bad string.

Otherwise (?&F2,?&F3)+Y points to the first non-space character, which is returned in A. Z is set if this is CR, indicating an empty, unquoted string. GSREAD will return characters until CR or space (if C=0 to GSINIT), or CR only (if C=1 to GSINIT) is reached.

It is safe to call GSREAD at least once following GSINIT.


The character returned by GSINIT is not necessarily the character returned by the first call to GSREAD.

Calling from BBC BASIC

Entry points

  • 6502 Entry Address: &FFC2 (I/O processor only)

Regregex (talk) 17:53, 11 January 2019 (CET)