Commodore Plus 4 - Page 435

Appendix G
Plus/4 Memory Maps
Three different maps are presented. The first describes each of the registers of the
graphics chip. The second gives an overview of the Plus/4's memory usage. The
third gives as much detail as possible about each location in the Plus/4.
Graphics Chip Register Map
The graphics chip is located at $FFOO-$FF1F (65280-65311). The usage of each
register is described as completely as possible.
Hexadecimal
$FF00
$FF01
$FF02
$FF03
$FF04
SFF05
$FF06
$FF07
Decimal
65280
65281
65282
65283
65284
65285
65286
65287
Bits
0-7
0-7
0-7
0-7
0-7
0-7
0-2
3
4
5
6
7
0-2
3
4
5
6
7
Function
Low byte of reload value for timer 1
High byte of reload value for timer 1
Low byte of start value for timer 2
High byte of start value for timer 2
Low byte of start value for timer 3
High byte of start value for timer 3
Vertical screen scroll position
0 = 24 rows, 1 = 25 rows
0 = blank screen, 1 = display screen
Bit map mode: 0 = off, 1 = on
Extended color mode: 0 = off, 1 = on
TEST (should always be cleared to 0)
Horizontal screen scroll position
0 = 38 columns, 1 = 40 columns
Multicolor mode: 0 = off, 1 = on
Flashing: 0 = yes, 1 = no
TV standard: 0 = PAL, 1 = NTSC
Reverse characters through hardware:
0 = yes, 1 = no
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