M69000 Asiliant Technologies, M69000 Datasheet - Page 154

• Manufacturer Part Number: M69000
• Manufacturer: Asiliant Technologies

Specifications of M69000

• Lead Free Status / Rohs Status: Supplier Unconfirmed

Chapter 12
Attribute Controller Registers
Unlike the other sets of indexed registers, the attribute controller registers are not accessed through a
scheme employing entirely separate index and data ports. I/O address 3C0h is used both as the read and
write for the index register, and as the write address for the data port. I/O address 3C1h is the read address
for the data port.
To write to one of the attribute controller registers, the index of the desired register must be written to I/O
address 3C0h and then the data is written to the very same I/O address. A flip-flop alternates with each
write to I/O address 3C0h to change its function from writing the index to writing the actual data and back
again. This flip-flop may be deliberately set so that I/O address 3C0h is set to write to the index (which
provides a way to set it to a known state) by performing a read operation from Input Status Register 1 (ST01)
at I/O address 3BAh or 3DAh (depending on whether the graphics system has been set to emulate an MDA
or a CGA).
To read from one of the attribute controller registers, the index of the desired register must be written to I/O
address 3C0h and then the data is read from I/O address 3C1h. A read operation from I/O address 3C1h
does not reset the flip-flop to writing to the index. Only a write to 3C0h or a read from 3BAh or 3DAh, as
described above, will toggle the flip-flop back to writing to the index.
&+,36
AR00-AR0F
Name
AR10
AR11
AR12
AR13
AR14
69000 Databook
Function
Color Data Registers
Mode Control Register
Overscan Color Register
Memory Plane Enable Register
Horizontal Pixel Panning Register
Color Select Register
Subject to Change Without Notice
Attribute Controller Registers
read/write
read/write
read/write
read/write
read/write
read/write
Access
Revision 1.3 8/31/98
Index
00-0F
10
11
12
13
14
12-1