Commodore Amiga A500 Technical Reference Manual page 212

AGNUS NOTES
BIT# SYM
15-08 EV7-EV0
07 ATT
06-04 X
02 SV8
01 EV8
00 SH0
VPOSR
VPOSW
BIT# 15,14,13,12,11,10,09,08,07,06,05,04,03,02,01,00
USE LOF
LOF=Long frame (auto toggle control bit in BPLCONO)
VHPOSR
VHP0SW
BIT# 15,14,13,12,11,10,09,08,07,06,05,04,03,02,01,00
USE V7 V6 V5 V4 V3 V1 V0,H8 H7 H6 H5 H4 H3 H1
RESOLUTION = 1/160 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.
209
FUNCTION
End (stop) vert.value.low 8 bits
Sprite attach control bit (odd sprites)
Not used
Start vert, value high bit
End (stop) vert, value high bit
Start horiz. value low bit
Read vertical most significant bit (and frame
flop)
Write vertical most significant bit (and frame
flop)
Read vertical and horizontal position of beam
or lightpen
Write vertical and horizontal position of beam
or lightpen
V8