Control Data Corporation INFORMATION SYSTEMS TERMINAL II Hardware Maintenance Manual page 94

The addressing is formed as follows:
• The lower 9 bits define the line position, with
a
0000 0000 at the top. The desired location is 9
dots away from the top the line address is:
A8 - AO
=
a
0000 1001
• The column address defines groups of 8 bits in the
horizontal direction, with 00 0000 on the extreme
left. The desired location is 21 dots away from the
left, the column address is:
•
A14 - A09
=
21/8
=
2 (Remainder
=
5)
A14 - A09
=
00 0010 (Data Bit 5)
By dividing the X coordinate by 8 it can be seen
that the integer result defines the column and the
remainder defines the Data Bit to be used in the
manipulation.
Address Bit 15 must be set to select the refresh
memory address.
The complete address is:
Address
=
1 000010 00000 1001
=
1000 0100 0000 1001
=
8409 1 6
The Read/Write instruction affects 8 bits at the time.
Only the Data Bit 5 must be altered, the following masks
are generated.
Write Mask
=
0010 0000 (DBs set)
=
20 1 6
Erase Mask
=
1101 1111 (DBs clear)
=
DF16
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