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Re: CB030, A 68030 SBC for hobbyists [message #7497 is a reply to message #7496] Sun, 12 April 2020 04:28 Go to previous messageGo to previous message
plasmo is currently offline  plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA
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Earlier on I didn't know how to automatically select different size SIMM72 memory so the size select was for selecting 16meg or 64 meg SIMM, but since then I have figured out memory size can be automatically selected by interleaving the high order addresses in the row and column addresses mux. So the size selection jumper is no longer in use.

In SIMM72 the byte selects are done with CAS0/1/2/3. RAS0/RAS2 select low/high 16-bit words of one bank while RAS1/RAS3 select low/high 16-bit words of the 2nd bank. 4/16/64meg SIMM have one bank, 8/32/128meg SIMM have two banks. Tying RAS0&RAS2 means the full 32-bit long word of a bank is always enabled which probably draw more power, but does save me a pin.
Bill
 
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