BASIC PROGRAMMING
SECTION 4.8
4.8.4
VER.V09F
To set up outgoing data the ARG reserved word is used, format as
shown. The variable will be equated to the value in brackets.
A
= ARG(5)
will cause the NSCBOO internal registers C and E to be set up as
follows:-
C = 5
E = 0
The pair are set up as a 16 bit integer, hence:-
ARG ( 10*256+30)
causes:-
C
= 30 and:-
E
= 10 (decimal)
when CALL is executed.
These registers are used for compatibility with the CP/M style
system call structure.
To return data to Basic the program:-
1000 X
= CALL (addr)
causes the value of variable X to take on the value contained in
register A.
PASSING MULTIPLE VARIABLES
To pass more than one integer between a 'CALLed' program and
Basic the machine code linkage stack is used.
This is controlled in Basic by PllSH and POP. In the routine:-
1000 PUSH X,Y
1010 A
= CALL. (addr)
1020
Y = POP(1)
1030 X
= POP( 1)
The integer values of X and
Y are first placed on the stack and
made available to the called routine, and then removed by the
POP instruction back into their own variables.
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