4004 and IC history / was Re: Vintage computer photogallery
dkelvey at hotmail.com
Sun Oct 14 11:47:41 CDT 2007
> From: hilpert at cs.ubc.ca
---snip---> > - RAM: no provision it appears, so you still need a 4002 > (or get by with registers, or via I/O)
It looks like one would need to build a full bus monitor. One
would no longer need the 4008/9 since one could use the
same circuit to moitor all.
The way the ROM and RAM chips work is that they watch the
instructions on the bus, going to the processor. When they see
instructions that require specific actions, they then execute
that operation on the bus.
As an example, if they see a write to RAM, the RAM chip
sees the instruction and then does the write at the correct
One can use the circuitry used for the EPROM on the SIM4-01
as an example of how to monitor the instruction flow.
With some extra work, one doesn't need 4002s.
They do show up on ebay now and then. Do remember, there
are two types. There are 4002-1s and 4002-2s The enable
is inverted so these can be used on the same select line.
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