THE
COMPARISON
ENABLE
BITS
Bits
14-1
are normally set
to
all Is. The use of the comparison enable bits is described
later in the "Advanced Topics" section.
Using
the
Copper
Registers
There are several machine registers and strobe addresses dedicated to the Copper:
o Location registers
o Jump address strobes
o Con trol register
LOCATION
REGISTERS
The
Copper has two sets of location registers:
COP1LCH High 3 bits of first Copper list address.
COP1LCL
Low
16
bits of first Copper list address.
COP2LCH High 3 bits of second Copper list address.
COP2LCL
Low
16
bits of second Copper list address.
In accessing the hardware directly, you often have
to
write
to
a pair of registers
that
contains the address of some data.
The
register with the lower address always has a
name ending
in
"H"
and contains the most significant data, or high 3 bits of the
address.
The
register with the higher address has a name ending in
"L"
and contains
the least significant data, or low
15
bits of the address. Therefore, you write the 18-bit
address by moving one long word
to
the register whose name ends
in
"H."
This
is
because when you write long words with the
68000,
the most significant word goes
in
the
lower addressed word.
In the case of the Copper location registers, you write the address to COP1LCH. In the
following text, for simplicity, these addresses are referred
to
as
COPILC
or COP2LC.
Coprocessor Hardware
13
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