The BBC and Master Computer Public Domain Library

BE41 Get Filename and set parameter block Filename and Load address

Submitted by Steve Fewell

Routine:Get Filename
Name: Get Filename and set parameter block Filename and Load address
Starting Address: &BE41
Entry criteria: BASIC Text Pointer A points to a String expression.
Exit: X and Y contain the High Order address (X = MSB). &3B-&3C = the High Order address.

Description:

[BE41] Call &BE36 to do the following:
* Set BASIC Text Pointer B offset to BASIC Text Pointer A offset.
* Get result of expression at BASIC Text Pointer B.
* Issue 'Type mismatch' error if the result is not a String value.
* Call routine &BE25 to Store a carriage return (#&0D) character at the end of the String, and to set &37-&38
to point the the SWA address (&0600).
* Call &9B91 to check that the Statement is terminated correctly.
This obtains the filename specified and appends a <CR> to the end of the name, so that the filename is in the correct
MOS format - ready for an operating system call to OSFILE (&FFDD) [which requires a <cr> to terminate the filename].
The OSFILE parameter block filename address field (&37-&38) is set to point to the filename (located in the SWA).

Store the Ptr A Offset value (in Y) minus 1 in location &39 - this value will be &00, as the Check end of statement
routine resets the PTR A offset to 1. This is the load address (LSB) parameter in the OSFILE parameter block.
Store &18 (PAGE -> MSB Byte) in location &3A. This is file load address (MSB) parameter in the OSFILE parameter block.

[BE4B] Read the Machine's High Order address (OSBYTE call #&82).
If no memory extensions are in place, the High order address will be &FFFF.
Store the High Order address in locations &3B-&3C (high byte first).
This sets the High Order location of the Load address in the OSFILE parameter block.
(now, locations &39-&3C contain the complete load address for the file).

Disassembly for the Get Filename and set parameter block Filename and Load address routine