Commodore Amiga A1000, Hardware Reference Manual

Page: 328 / 380

CHIP REGISTER MAP
Each 8520 has 16 registers that you may read or write. Here is the list
of register and the access addresses of each within the memory space
dedicated to the 8520:
Register
RS3 R52 RS1 RS0 (hex) NAME MEANING
------------------------------------------------------------
0 0 0 0 0 pra Peripheral data register A
0 0 0 1 1 prb Peripheral data regigter B
0 0 1 0 2 ddra Data direction register A
0 0 1 1 3 ddrb Direction register B
0 1 0 0 4 talo Timer A low register
0 1 0 1 5 tahi Timer A high register
0 1 1 0 6 tblo Timer B low register
0 1 1 1 7 tbhi Timer B high register
1 0 0 0 8 todlow Event LSB
1 0 0 1 9 todmid Event 8-15
1 0 1 D A todhi Event S
1 0 1 1 B No connect
1 1 0 0 C sdr Serial data register
1 1 0 1 D icr Interrupt control register
1 1 1 0 E cra Control register A
I 1 1 1 F crb Control register B
SOFTWARE NOTE:
The operating system kernel has already allocated the use of
several of the 8520 timers.
CIAA, timer A - keyboard (used continuously to handshake
keystrokes). NOT AVAILABLE.
CIAA, timer B - Virtual timer device (used continuously
whenever system Exec is in control; used
for task switching, interrupts and timing).
CIAA, TOD - 50/60 Hz timer used by timer.device. The
A1000 uses power line tick. The A500 uses
vertical sync. The A2000 has a jumper
selection.
CIAB, timer A - not used
CIAB, timer B - not used
CIAB, TOD - graphics.library video beam follower. This
timer counts at the horizontal sync rate,
and is used to synchronize graphics events
to the video beam.
Note that previous editions of this chart were incorrect.
- Appendix F 319 -