Discussion:
Apple II Bus question
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Anthony Ortiz
2017-10-03 05:12:33 UTC
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According to the following link :
https://allpinouts.org/pinouts/connectors/buses/apple-ii-slot/

The Apple II address and R/W lines are bi-directional (IN/OUT); is this true? In Sather's book the diagram on 4-3 shows them being uni-directional and the data lines as bi-directional.

Thoughts?
Michael J. Mahon
2017-10-03 07:04:49 UTC
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Post by Anthony Ortiz
https://allpinouts.org/pinouts/connectors/buses/apple-ii-slot/
The Apple II address and R/W lines are bi-directional (IN/OUT); is this
true? In Sather's book the diagram on 4-3 shows them being
uni-directional and the data lines as bi-directional.
Thoughts?
From the processor's viewpoint, the address lines are unidirectional, but
from the point of view of the bus, and things plugged into it, the address
lines are bidirectional, e.g.: DMA. DMA disconnects the address lines from
the processor.
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
Jorge
2017-10-03 09:17:14 UTC
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Post by Anthony Ortiz
The Apple II address and R/W lines are bi-directional (IN/OUT); is this true? In Sather's book the diagram on 4-3 shows them being uni-directional and the data lines as bi-directional.
Thoughts?
That url is the slot connector, but the Figure 4.2 in page 4-3 is the CPU, and the tri-state driver on the address lines of the CPU is there to disconnect its address lines from the bus when a slot card wants to drive them to do DMA.
--
Jorge.
Anthony Ortiz
2017-10-03 12:17:20 UTC
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Thanks guys! :)

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