Submitted by Steve Fewell
Set A to #&C0. This is the OSFIND (&FFCE) option to open a file for update/random access.
Store A (the OSFIND option number) to the 6502 stack.
Call routine &AD36 to obtain the value after the OPENUP keyword (this should be the filename to open).
If the result of the expression value is not a String value then issue a 'Type mismatch' error.
Call routine &BE2B to store a carriage return character at the end of the SWA (as the OSFIND operation requires the
filename to be terminated by a '<cr>' character.
Set X to #&00 and Y to #&06, so that X & Y point to the filename (i.e. the SWA location - &0600).
Retrieve the OSFIND option from the 6502 stack.
Call the Operating System OSFIND routine to perform the file open operation and return the channel number that the file
was opened on in A.
Jump to routine &AE18 to set the IWA to the 8-bit value in A (i.e. the channel number of the opened file).
This causes this routine to return the channel number value - which is usually then assigned to a variable by the BASIC
|AAE7||169 192||A9 C0||LDA#&C0|
|AAEA||6||032 054 173||20 36 AD||JSR &AD36 Get value / result of expression (if bracketed)|
|AAED||208 013||D0 0D||BNE 13 --> &AAFC|
|AAEF||+||032 043 190||20 2B BE||JSR &BE2B Store #&0D (carriage return, '<cr>') at the end of the SWA value|
|AAF2||162 000||A2 00||LDX#&00|
|AAF4||160 006||A0 06||LDY#&06|
|AAF7||032 206 255||20 CE FF||JSR &FFCE OSFIND|
|AAFA||128 198||80 C6||BRA -58 --> &AAC2 [JMP &AE18 Set IWA to the 8-bit value in A]|
|AAFC||L||076 146 144||4C 92 90||JMP &9092 Type mismatch error|