5.5 Zero Page Locations
CP
1M
holds a number
of
parameters in page zero
of
the main memory bank.
The IOBYTE (section 5.2)
is
held in location 3H. The following are important
locations in page zero. Further information
is
included in the books referred
to
in Chapter 3, and other such books.
Location in hex
Contents
from to
0000
0002
A
jump
instruction followed by the warm
start entry address. Thus locations
0001
and 0002 contain WBOOT.
0003
The IOBYTE. See section 5.2 for further
details.
0004
The current default drive number
(0
= A:,
1
=B:
etc.)
"
0005
0007
A
jump
instruction followed by the loca-
tion
of
BDOS. Thus locations 006 and 007
contain the lowest address used by
CP
1M.
5-8
5.6 The BIOS Interface
The Basic Input/Output System (the BIOS)
of
the operating system for the PX-8
includes many useful subroutines which can be used by calling their entry ad-
dresses from user programs after setting parameters (if required) in applicable
registers. Care must be taken
to
ensure
that
the entry addresses are correctly
specified when calling these subroutines.
5-9
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