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   Author  Topic: ULA Schematics  (Read 130 times)
ronpro
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ULA Schematics
« on: Mar 22nd, 2007, 8:43am »
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I've seen schematics for zx80, zx81, ts1500.  Do schematics exist for the ULAs in any of these machines?
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wilf_zx
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Re: ULA Schematics
« Reply #1 on: Mar 23rd, 2007, 1:08pm »
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There are no schematics for the original TS1000/ZX81 or TS1500 ULAs. The internal circuits of those are enhanced versions of the original ZX80 circuit. The ZX81 circuit used a number of  RC components for delays and deglitching.  The ZX97 and  derivatives used an all digital circuit.  Bodo has designed a "super ULA" using a FPGA for which a logic file is available.
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Re: ULA Schematics
« Reply #2 on: Mar 23rd, 2007, 2:24pm »
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How were people able to develop machines like the zx97, etc. without schematics?  Was the ULA reverse engineered?
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wilf_zx
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Re: ULA Schematics
« Reply #3 on: Mar 27th, 2007, 3:54pm »
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Not so much a reverse engineered ZX81 as an enhanced  ZX80 clone which schematic was the basis for the ZX97 design.  
 
Unlike the ZX80 which used a sprinkling of capacitors to get the timing right,  I designed the ZX97 to be all digital and be ZX81 SLOW mode compatible.
 
The whole design process was documented on Jack Raats' mailing list group as a communal blog with input and comments from many people in the group.  In some cases, I was able to add  items from the wish list to the ZX97 design at virtually no extra cost.  
 
I also incorporated into the ZX97, many of my previously published sub circuits such as the 74HC251 memory decoder/address mapper to take advantage of the larger memory chips available  in 96/97.  
 
The  main design objective  of the ZX97 was to use the simplest possible circuit design to provide the maximum possible features.  
 
Unlike the ZX81 with its ULA blackbox, the ZX97 is a well documented discrete logic design.  
 
While it is feature rich as is, the ZX97 can be easily modified as required for example like the ZX97lite design which was simplified to permit a single layer PCB layout.
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