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Communication Between BASIC and Assembly Language
131
Calling Procedure:
1.
Load register B with the address of the pseudo-instruction of the common declaration to
be checked.
2. Call the utility.
Exit Conditions: The utility returns the busy bits in the A register. The "read" busy bit is in bit
o
and the "write" busy bit is in bit 1. The other bits are not disturbed.
In the following example, if any of the busy bits among three common variables is set, a flag is
set and the routine is exitted -
ISrnJRCE
V~riab121:
INT
ISOURCE
Variable2:
SHO
ISOURCE
Variable3:
REL
I
:::;Ci!JF~~
C:E
its. :
I i'··j'r
I ::::;QURCE
::;;01····1:.
~
L..DE:
::::"/::lx···i
.:::;.b·\
e
1
I :::OU
F~~CE
I ::::Di...iF:CE:
I
:::;Oi.JF:CE
I:::CUPCE
ISCURC:E
I ::;CitJ
I:~~C:E
I
::;OUF:CE
ISOUF:CE
I::;OURCE k:!t-+:
::;
~~F
. : , : .
+4
LDfi :::::::1
LDE
Bu~:.':..'
b·i
t :::.
Cor~inue
processing
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