AGNUS NOTES
BIT# SYM
-
FUNCTION
15-08 EV7-EVO End (stop)
vert.value.low
8
bits
07
ATT Sprite attach control bit (odd sprites)
06-04
X
Not used
02 SV8 Start vert. value high bit
0 1 EV8 End (stop) vert. value high bit
00 SHO Start horiz. value low bit
VPOSR
Read vertical most significant bit (and frame
flop)
VPOSW
Write vertical most significant bit (and frame
flop)
BIT# 15,14,13,12,11
,l
0,09,08,07,06,05,04,03,02,01,00
USE LOF
V8
LOF
=
Long frame (auto toggle control bit in BPLCONO)
VHPOSR
Read vertical and horizontal position of beam
or
lightpen
VHPOSW
Write vertical and horizontal position of beam
or
lightpen
BIT#
15,14,13,12,11,10,09,08,07,06,05,04,03,02,01,00
USE
V7
V6
V5
V4
V3
V1 VO,H8
H7 H6
H5 H4 H3
H
1
RESOLUTION
=
111 60 OF SCREEN WIDTH
(280
NS)
1) The Agnus pointer registers are updated via a pipelining scheme
that requires that a register not be accessed on two contiguous
cycles.
This precludes the use of "single operand"
blitter functions that
might seem possible based on the register descriptions.
Caution is also required to prevent processor access to registers
that may be subject to concurrent
DMA
access.
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