Commodore 128 Programmer's Reference Manual page 343

PROGRAMMING THE 80-COLUMN (8563) CHIP 333
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be configured to be compatible with 4164 8563 RAMs (64K by 1) or with 4416 8563
RAMs (16K x 4). Register 28, bit 4 should be initialized to a 0 for operation with
4416s a 1 for operation with 4164s.
4416: Row/Col = A7/A15, A6/A13, A5/A12, A4/A11, A3/A10, A2/A9, A1/A8,
A0/A8
4164: Row/Col = A7/A15, A6/A14, A5/A13, A4/A12, A3/A11, A2/A10, A1/A9,
A0/A8
R28(7-5) CHARACTER SET START ADDRESS
The starting location of the character set in display 8563 RAM is determined by
R28(7-5). These bits form the most significant 3 bits of the 16-bit address used to
access character data. If R9(4-0) is greater than 15, then only bits 7-6 of R28 will be
used, because each character set will occupy 8192 bytes of 8563 RAM memory.
The character pointers correspond to a displayed character position on the frame.
The 8-bit pointer selects one of the 256 characters in the character set to be displayed at
that position on the frame. For a frame of i rows of j characters each, the first j pointers
will define the characters in the first (top) character row, and (i x j) pointers will need
to be defined in display 8563 RAM. For 25 character rows of 80 characters each, 2000
pointers will be needed.
R29(4-0) UNDERLINE SCAN LINE COUNT
The number of the scan line used for underline. The underline is defined as a single scan
line. Scan line 0 refers to the scan line at the top of the character.
R32, R33 BLOCK COPY SOURCE ADDRESS
Block Copy is similar to Block Write, except that the data written to 8563 memory is
obtained from other successive memory locations. The Block Copy actually 'copies'
one part of 8563 memory to another. To set this operation up, the CPU writes the initial
Destination Address to R18/R19, waits for the Update Ready Status bit to be 1 and
writes a 1, to R24(7) selecting the Block Copy mode. The CPU then writes the initial
source address to R32 (most significant byte) and R33 (least significant), then the
number of successive memory locations to be copied should be written to R30. The
8563 will then read the contents of the first source address and write that data to the first
destination address. Additional copies will occur at addresses incremented from the
source and destination addresses, for as many words as are defined in R30.
R34, R35 DISPLAY ENABLE BEGIN, END
During the horizontal and vertical synchronization pulses, the R, G, B and I signals must
be blanked (brought to a low level) to prevent the display of the scanning beam during
retrace times. Two registers allow the user to adjust the beginning (R34) and end (R35)
of the horizontal blanking interval.
Register R34 is programmed with the number of characters from the first dis-
p played character of a row to the first blanked character in that row. Register R35 is
j ) programmed with the number of characters from the first displayed character of a row to
the last blanked character in that row. Blanking occurs on all scan lines of a frame.