!MENU - A Program Menu for the BBC Microcomputer
This document and the program described in it are copyright (C) 1989-1995,
Angus J. C. Duggan.
A tar archive containing a PDF version of this document and
the program itself is available from
This document describes a machine code program which provides an
easily configurable menu of the programs on a disc. The program program is
normally called from the auto-boot file !BOOT by pressing SHIFT and
BREAK together. When the program is called, it reads data from the
current input stream (usually the *EXEC file from which it was called), and
produces a menu of program titles which can be selected from using the cursor
keys and RETURN.
The menu program is extremely simple to operate. When the menu
display appears initially, the first entry is highlighted. The up and down
cursor keys can then be used to move the highlight to the desired entry, and
the return key can be used to execute it. If there are more choices than the
screen can display, the message * * * more * * * is displayed at
top and/or bottom of the menu, depending on whether the highlight is at the
top, middle, or bottom of the list. If the message disappears when a cursor
key is pressed, there are no more entries to be found in that direction, and
the highlight will move no further. At any time, the `S' key can be used
to toggle the sound on and off, and an indicator on the bottom line of the
display changes to show whether the sound is currently on or off. Note that
some programs may turn the sound on when they are run, in which case this
toggle will be ineffective.
!MENU program is normally called as the first line of a *EXEC file on
auto-boot, but new menu entries can be tested by calling the program from the
The data which the program reads should be normal ASCII text with
carriage returns at the end of each line. Files produced by
VIEW or by *BUILD are suitable.
- Menu format
- Calling the program
- Errors detected
- Memory usage
If the first character of a line is a backslash, then the
rest of the line is ignored. This allows comments to be inserted into the
configuration file. Blank lines and lines with only spaces and tabs are
also ignored, and can be used to improve the readability of the file.
Lines which start with a space or a tab character and have other
characters on them are command lines. When a program is selected from the
menu, these lines define the commands which run the program. The commands can
include complex operations such as loading multiple sections and relocating
files. The command lines may include escaped characters, which will be
translated into control characters when the command is executed. The escape
symbol `|' is inserted into a command by doubling it to `||'. A
maximum of ten command lines including both the common command lines and the
menu selection command lines is allowed, and a minimum of one command line is
imposed. There is a further restriction on the maximum number of characters in
all the commands, which should be less than 238. This number does not include
the leading spaces and/or tabs on the command lines, which are stripped off
All of the other lines which start with visible ASCII characters
are title lines. These lines define the names of the menu
selections, and of the title banner. Each title line precedes the commands
which are associated with it.
The first title line in the input data is a special entry which
defines a title banner that appears at the top of the screen in double height
characters. The commands associated with the first title are common to all of
the menu selections, and are executed before the entry's associated commands
when the menu entry is selected. Titles may be a total of 32 characters long,
including any spaces within them, and there can be a maximum of 64 titles, and
a minimum of 2 titles (including the banner) in one menu.
The last line of the input data should contain a single full stop
`.' and no more.
The program will detect some error conditions, including operating
system errors. When an error is detected, the error message is printed,
and the program tidies up cleanly before executing.
The errors which can occur are:
The auto-boot program is assembled at address &7000, and so should
run on most BBC configurations, but its presence in this area may corrupt
some language program areas. This is why one command is enforced for each
selection, so that a language can be initialised safely. The configuration
data is stored from OSHWM upwards, and should not cause any
problems unless it is huge.
The program uses the Econet workspace in &90-&9F, but this should
not cause problems because the program is intended for disc based systems.
Note that the user-defined keys 0-9 are also used and should not be
redefined in the commands. Keys 10-15 can be defined if there is enough
space for the definition.
A simple example of an *EXEC file is given to illustrate the
points already discussed.
- This error should not happen, because the escape key is disabled by the
program, but it is trapped anyway.
- Line too long
- This error happens when more than 256 characters are found without a
carriage return separating them. This usually means that the input stream
- No commands
- If a menu entry is selected which has no associated commands, and there
are none associated with the banner, this error occurs.
- Title missing
- This error happens if command lines are found before a title line has
- Title too long
- This error occurs if a title line contains a title which is too long to
fit on the screen. The maximum length of title lines is 32 characters.
- Too few entries
- There must be at least one selectable entry in the menu. This error
occurs if there were too few titles found.
- Too many commands
- This error occurs if there were more than 10 commands given for a
program, including the common banner commands.
- Too many entries
- This error happens if the configuration file contains more titles than
are allowed. The limit is 64 titles, including the banner.
\ Title of disc comes first
Demo Disc (C) AJCD 1986
\ All programs require escape enabled
\ Titles of programs come next
\ Exit to VIEW
\ use escape characters to change mode
\ Exit to BASIC
\ And a demonstration of relocation
\ (only works if you have a *move command)
Countdown to Doom
*LOAD B.COUNT 1900
*MOVE 1900 E00 +6400
\ end of demonstration file
Centre justification can look untidy depending on the order of the
filenames in the menu, and can be tidied up by adding spaces to the end of
Last modified on 12th February 2004 by firstname.lastname@example.org