Everything You Always Wanted To Know
But Were Too Polite To Ask
Amiga Technical References
Amiga 2000 Jumper Settings
These setting come out of the manual for an Amiga 2000 Revision 4.x and is compliant with REV6.x Amiga 2000 boards as well.
- This jumper determines the high order address bit for Fat Agnus.In it's
normal position, the high-order bit is A23; in it's other position, this bit
is A19. The current Fat Agnus chip requires the A23 signal for proper
management of the memory at $C00000. Future Fat Agnus chips may may things
differently; this keeps the current board compatible with simple
- This jumper is used to set the light-pen port number. In the 2-3 position,
the light pen input will be the FIRE input of the mouse/joystick port 0.
With the jumper in the other position, the light pen input will be the FIRE
input of mouse/joystick port 1.
- This jumper determines the time base used for the 50/60Hz CIA timer chip.
In the normal posistion, the 50/60 TICK clock, based on AC line frequency,
is used as a time base. In the alternate position, the verticle sync pulse
from the video section is used. The system will not operate properly without
one of these clocks.
- This jumper is closed to add a second internal floppy drive, open to leave
the second floppy out of the main unit box. The Amiga expects an ID bit
stream from each floppy drive; this lets it determine the drive type.
External floppies have this ID circuitry on board, but as it's not an
industry standard capability, it has to be implemented on the A2000
motherboard to save cost on internal drives. Leaving the jumper open
prevents the Amiga from seeing the ID sequence.
- This jumper is used to enable the 512k of RAM at $C00000 and the real-time
clock. It is normally closed; opening it will disable both this extra RAM
and the real-time clock.
Copyright © 2000 Amiga Auckland Inc. All rights reserved.
Revised: August 13, 2005.