SC/MP 8073 addressing query

Allison ajp166 at verizon.net
Wed Jan 28 14:31:25 CST 2009


Doug if you want the info email me direct.  It's scans of relevant parts 
of the manual.


Allison


Doug Jackson wrote:
> Hi Alison,
>
> Just a quick re-send in case you didn't get the original request.
>
> Are you able to shed come light on the configuration bits you 
> mentioned below?  (I was aware of the baud rate bits, but have no 
> knowledge of the boot from ROM bit you mentioned)
>
> Also a quick scan of the demo board would be awesome.
>
> Thanks,
>
> Doug
>
> Allison wrote:
>>> Subject: SC/MP 8073 addressing query
>>>   From: Doug Jackson <doug at stillhq.com>
>>>   Date: Wed, 21 Jan 2009 09:26:13 +1100
>>>     To: General Discussion: On-Topic and Off-Topic Posts 
>>> <cctalk at classiccmp.org>
>>>
>>> Hi list,
>>>
>>> I have an interesting question regarding the INS8073 (National 
>>> Semiconductor SC/MP 3 with BASIC in ROM).
>>>
>>> Finally, somebody gave me a round tuit, and I have started work on a 
>>> simple 8073 system.
>>>
>>> Eventually, it will have 8K of ROM, 8K of RAM, an 8255, and a switch 
>>> / LED interface. Currently on the board, I have the 6264 RAM tied to 
>>> the 8073, with no address decoding (ie the CS* on the RAM is tied to 
>>> A15 on the CPU).  Sadly, as a simple test, this does not operate as 
>>> I would expect.  I would have expected that the RAM would have been 
>>> selected anywhere in the lower 32K or the memory map, and I would 
>>> have a simple system that would spit out a console prompt.  But no 
>>> luck.
>>>
>>> Now the question....  The internal ROM is located in the lowest 4K 
>>> or the memory map.  When the CPU is fetching data from the lower 4K, 
>>> does it assert the NRDS line, and sample the external bus?  My 
>>> belief is that it does not, as the trivial application note that I 
>>> have seen simply ties a couple of 2114 to the processor, and uses 
>>> A10 as the chip select.
>>>
>>>     
>>
>> I built one years ago and pull it out frm time to time.
>>
>> No, it's less than 4K and yes you do get NRDS.
>> Also you need pull up resistors on selected lines to set baus rate 
>> and boot on rom.
>>
>> I'd use 2116(2kb) or 2164s(8kB) as they are 8bits wide and really 
>> save on parts and power over 2114.  One 2164 placed at at 1000h makes 
>> for a tiny sysem.
>>
>> Finally NIBLE when it starts does a memory check for (Ep)rom at 8000h.
>> There are some addresses that are tested for information that have to 
>> be respected.
>>  
>> If no one comes up with the circuit that National had for the demo 
>> board they sold  I can scan my copy, it's pretty poor but may help.  
>> The manual
>> is just too thick for me to scan or copy.
>>
>>
>> Allison
>>
>>  
>>> Any ideas?
>>>
>>> Doug
>>>
>>>
>>>
>>> -- 
>>> Doug Jackson, I-RAP, MAIPM, MIEEE
>>>
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>>>     
>>
>>   
>
>




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