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jasonsbeer / Amiga-2000-EATX

An Amiga 2000 PCB in the EATX form factor.
GNU General Public License v3.0
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Buster _D2P Pull Down #32

Closed jasonsbeer closed 1 year ago

jasonsbeer commented 1 year ago

Starting with revision 6.2, the Commodore A2000 board incorporated a pull down data bus. Due to the way it was implemented, this added a pull down to the direction signal on the Zorro 2 data bus buffers. This pull down is not necessary, but apparently has not caused any issues (?). Consider removing it.

jasonsbeer commented 1 year ago

It would be best to replace this with a pull up resistor. In the event Buster is absent, or otherwise failing in a specific way, the data buffers between Zorro 2 and 68000 will be going in the wrong direction. This will cause a failure to start condition due to data bus contention. To aid in troubleshooting (if it should be necessary), these buffers should be held in the 68000 -> Zorro 2 state.

It would be beneficial to add a pull up to _DBOE for the similar reasons.

jasonsbeer commented 1 year ago

Added a pull up to _DBOE in Revision 3.0. That should cover it.