8-Bit Software

The BBC and Master Computer Public Domain Library

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8F83 Prompt for command line and execute the entered command(s)

Submitted by Steve Fewell

Description:

If called from &8F83 then a full initialisation will be done before the command line prompt appears.

This will reset the following:: * Program start address; * Stack Pointer; * Clear *EDIT mode; * REPEAT/FOR/GOSUB parameters, return addresses, etc...; * Page &7 user tables (&07F0-&07FF); * Variable pointer tables (destroys all variables that have been created)

If called from &8F86 then the initialisation will not be done as not required. Any defined variables (etc...) will remain

Reset the BASIC Text pointer A (&0B, &0C) to &0700 (the address of the command line buffer).
Call routine &B2A6 to reset the 'ON ERROR' pointer to BASIC's default error handling routine.

Call OSWRCH with A = #&3E to output the '>' [prompt character] to the screen.
Call routine &BA74 to read the input line (using OSWORD 0) and store the input to the command line buffer (&0700-
&07EF). The parameters (line length, minimum and maximum acceptable characters, etc...) for this input as the same as
those used during the INPUT command (as both inputs are done by the same routine, (&BA70)).

[&8F97] Set the 6502 stack pointer to #&FF (to clear any FN/PROC subroutines that were in progress when the last
command (that was executed by the BASIC Intrepreter) had finished, or when the last program execution had ended).
Call routine &B2A6 (again) to reset the 'ON ERROR' pointer to BASIC's default error handling routine.

Call routine &BAEB to tokenise the command line (&0700-&07EF) and to enter the line into the current BASIC
program if a line number was supplied at the start of the command line.
If the Command line contained a program line (which has now been inserted into the current program), then jump back
to &8F83 to do a full initialisation (as after a line in the Program has been inserted/changed or removed, any defined
variables need to be reset, because the TOP of the program has now been changed - corrupting the variable storage space).

Otherwise, if a direct command (not a program line) has been entered, then call &901E to execute the statement(s) on
the Command Line.

Disassembly for the Prompt for command line and execute the entered command(s) routine

8F83		032 172 187	20 AC BB	JSR &BBAC Initialise Page 7 & reset Variable pointers, etc...
8F86		160 007	A0 07	LDY#&07
8F88		132 012	84 0C	STY &0C
8F8A	d	100 011	64 0B	STZ &0B
8F8C		032 166 178	20 A6 B2	JSR &B2A6 Reset 'ON ERROR' pointer to BASIC's default error handling routine
8F8F	>	169 062	A9 3E	LDA#&3E
8F91		032 238 255	20 EE FF	JSR &FFEE OSWRCH
8F94	t	032 116 186	20 74 BA	JSR &BA74 Prompt for & get the User's input line (storing it in buffer &0700-&07FF)
8F97		162 255	A2 FF	LDX#&FF
8F99		154	9A	TXS
8F9A		032 166 178	20 A6 B2	JSR &B2A6 Reset 'ON ERROR' pointer to BASIC's default error handling routine
8F9D		032 235 186	20 EB BA	JSR &BAEB Tokenise Command Line and Insert Line into Program (if line number given)
8FA0		176 225	B0 E1	BCS -31 --> &8F83 Initialise & prompt for next command line
8FA2	z	128 122	80 7A	BRA 122 --> &901E Execute the command line