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
- 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.