SYS-EX – A 1K extension program for NAS-SYS monitors – Part 3

by David G. Johnson

This article describes the second half of the commands available under SYS-EX, following on from the previous article.

q

Query tape contents

Read a cassette tape and display on the screen any tape labels as written by the “l” command, and any file names as written by the ‘w’ command or by the 8K Basic.

Each file name read is displayed on the next available screen line and, if necessary, the screen lines are scrolled in the normal way. The command is terminated by first stopping the cassette tape recorder and then typing four ESC (SHIFT:ENTER) characters. Four consecutive ESC characters read from the cassette tape input will have the same effect.

This command is one of the four SYS-EX commands that display tape labels (the others are ‘r’, ’s’ and ‘v’). Tape labels are always displayed within the first 42 character positions of the top line (line 16). Labels that are shorter than the 42 character maximum length are space filled up to the maximum length. Therefore, displayed tape labels overwrite the whole of the top line with the exception of the final six character positions, which are always left unaltered.

r

AAAA
--- required file name ---

Read named file

Read a cassette tape and search for a file name which matches with the required file name. When a match is found, read the file into memory using the NAS-SYS Read command.

After entry of the ‘r’ command, the prompt ‘rName:’ appears on the next screen line and the required file name is entered on that line. Optionally, ‘transparent’ characters may be entered as part of the required file name. A transparent character will match with any character read into that position. The transparent character is ASCII 7FH (Control:Shift:/).

The tape drive LED is switched on and the cassette tape is searched for tape and file labels. Any tape labels detected are displayed on the top screen line without interruption of the command. As each file label is detected, the file name is displayed on the screen line immediately below the required file name. Any file name or text which was previously displayed on that line is blanked