jcwren at jcwren.com
Fri Dec 30 23:19:07 CST 2005
Tony, you may want to ask in the cosmacelf group on yahoo.com. Bob
Armstrong and a few others are very knowledgable of the intimate details
of the 1802.
Tony Duell wrote:
>Does anyone really know the RCA 1802 processor hardware?
>I am still debugging the microwriter, and have not got very far. I have
>an RCA user manual on the processor which seems quite comprehensive, I am
>asusming it's accurate.
>Now, according to that manual, the processor can be in one of 4 states
>(fetch, execute, interrupt responze, DMA), and which state it's in is
>output on 2 lines called SC0 and SC1.
>The INT/ line is high, both DMA IN/ and DMA OUT/ are also high. I can
>detect no gltiches on any of these signals. The clock is running, the bus
>looks active, etc.
>The problem is that I am getting active-high pulses on SC1. This,
>according to the data sheet means it's doing a DMA or interrupt response
>cycle. But why the heck should it?
>I thought it was a defective 1802 chip, but another one pulled from an
>old board shows identical behaviour (right down to locking up after
>typing 8 characters on the microwriter keyboard). I can't believe 2 have
>failed in exactly the same way. Unless of course this is a well-known
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