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Old 14 December 2020, 02:23   #1
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Amiga 3000 without Daughterboard

I know one wont boot without a DB,

But the 4000 will...

I`ve been looking at the schematics on both, looking for the difference, expecting the A3000 DB to return a signal to inform its installed - where the 4000 does not... but I cant find it.

The only difference I can find (looking on vector schematics on AmigaWiki) is on the A3000, there is a D-flip/flop IC. Its controled by 2 clock signals from Agnus - but they are just clocks - so no detection input to Agnus here. The output from the flip-flop goes to pin 17 of the EDGE2 (86pin video port)
On the Mobo, this only goes through a capacitor to GND - so no detection of DB here either ?

What makes the A3000 know it has a daughterboard?
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Old 14 December 2020, 05:01   #2
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Might want to ask Hese, his AA3000+ works without the daughterboard.
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Old 14 December 2020, 11:44   #3
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Maybe it doesn't know, but it's a question of bus loading/reflections/etc?
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Old 14 December 2020, 12:33   #4
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A3000 requires a daughterboard due to the _DTACK signal. On the A3000 the signal is pulled up on the daughterboard, on the A4000 the signal is pulled up on the motherboard.

If you add a pull-up resistor to the A3000 motherboard between CN600 pin 66 and +5V, you can boot it without the daughterboard.
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Old 14 December 2020, 20:57   #5
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Thanks very much... what vaule resistor would you recommend?
_DTACK goes to a 220/330 to +v and GND on the daughterboard.

So I imagine 220 ohm?

Last edited by simon_m74; 14 December 2020 at 21:25.
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