Vax 613 0S Instruction Manual Page 327

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Table 78 summarizes how to perform each operation referencing an I/O register.
Table 78 How to Address I/O Registers
Operation Steps to Perform
Read 1-3 bytes from a
register.
Disable interrupts and exceptions; the IOSLOT register is a
shared resource.
Load the valid and byte mask bits into the IOSLOT register at
its alternate address (see Section 3.3.1)
Issue an LDL command to the register in its sparse I/O space
location.
Clear the Valid and Byte Mask bits in the IOSLOT register.
Reenable interrupts and exceptions.
Read a longword from
one register.
Issue an LDL command to the register at its sparse I/O space
location.
Read longwords from
two adjacent registers.
Issue an LDQ command to the register at its dense I/O space
location with the lower address.
Write 1-3 bytes to a
register.
Issue an STQ command to that registers sparse I/O space
location with the appropriate bytemask in the high longword
and the data in the low longword.
Write a longword to one
I/O register.
Issue an STL command to that register’s dense or sparse I/O
space location. You can also write a longword to it via an STQ
to that register’s sparse I/O space location, with a bytemask =
write all 4 bytes (0000).
Write longwords to two
adjacent registers.
Issue an STQ command to the dense I/O space location of the
register with the lower address.
A.6.2 Example of I/O Address Mapping
In the following examples, the user accesses the CXTurbo’s PLANEMASK_
ADDRESS register through both dense and sparse I/O space.
Address Mapping in Dense I/O Space:
The dense I/O space address is 1.E210.0028.
To read the register through dense I/O space, issue an LDL command to this
longword address:
03
: Longword PA
02 01 0029 28 27 263133 32
MR−0114−93RAGS
0 1 7 0 0 420005 0 XX
Bits <1:0> of the dense space address are ignored.
To write to the register through dense I/O space, issue an STL command to
the longword at the same address:
03
: Longword PA
02 01 0029 28 27 263133 32
MR−0114−93RAGS
0 1 7 0 0 420005 0 XX
Dense and Sparse Space A–7
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