HP 9835A Programming Manual page 172

152 I/O Handling
Mask necessarily contains the select code to be signalled. Rather than containing the number of
the select code, however, it has the bit set for the appropriate select code. For example, if you
are signalling select code 2, you set bit 2 to 1 in Mask and leave the others O. Similarly, if you
are signalling select code 5, you set bit 5. Thus, the statement containing Mask in the above
could just as easily be a literal. For example -
would signal select code 5.
When you want to signal a select code after others have already been signalled, a slightly
different instruction sequence is required -
I ::;Ol .. H<E
I :::ClUF:CE
I3C1UkCE
I::;OUPCE
r:::CUF:CE
T :::;OUF:CE
I::::Ol...IkCE
I::::OUF:CE
LDB I
::x·._P::;·I.,.1
LDA =10:?:::t:
::;TA :t:~ I
AIlE: =3
LIlA j·'1.a::;.k
DIk
TOP
Mask is the same as above.
Or·::;.
in the select code
As a further example, suppose you want both to signal BASIC when a device sends a line-feed
character to the computer, and to terminate the ISR's linkage. Then the ISR might appear as-
. _ . _ .iF:·········· L..r
~
:'_.'-',, .
J.~j
,~
,t
a line feed?
i :::.r'·'
[:::::1.:3:: i .
L ... 'ul:::
.L
.... ' , =;;;1
r··~3. ' 1 ~B A : : : : ; I C:
:::::j ..
,
.:.