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	                       MODIFICATION LEVEL SUMMARY		       
	  	     							        	  Product Code            P/N 520-0138-1          Product Type STDC/ZPU

	  Page 1 of               Date Issued 02/03/85           Revision C    
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	  Mod Level 0      Reference # 2.187        Date Released 06/21/84     
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	  Change: 1) Jumper S100-75 to IC52-15. Route jumper from S100-75 on
	  	     solder side through feed thru above S100-74 to IC52-15 on
	  	     component side.
	  	  2) Install 220pf C27 and 20pf C28 as legend indicates, but
	  	     with lower leads of caps inserted into lower holes of
	  	     option block.

	  Reason: The dedicated jumper pads for ZPU option all have internal
	  	  shorts. This modification bypasses the shorted traces.
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	  Mod Level 1      Reference # 2.349        Date Released 07/31/84     
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	  Change: 1) The S100 priority interrupt connector should be marked with	  	     yellow paint on the right side (PRI OUT).

	  Reason: 1) Color coding simplifies the connection of the priority
	  	     interrupt cable.
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	  Mod Level 2      Reference # 2.401        Date Released 08/16/84     
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	  Change: 1) Replace STDC ROM (502-0106-1) at IC26 with 502-0106-2.

	  Reason: 1) Update STDC firmware to version 1.16
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	  Mod Level 3      Reference # 2.439        Date Released 08/17/84     
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	  Change: 1) Replace STDC ROM (502-0106-2) at IC26 with 502-0106-3.

	  Reason: 1) Update STDC firmware to version 1.17.
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	  Mod Level 4      Reference # 2.456        Date Released 08/27/84     
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	  Change: 1) Change R32 from 1K to 330 ohm (001-0012).
	  	  2) Change C20 from 33pf to 75pf (004-0007).

	  Reason: Corrects circuit values for Q2 and Q3 from new vendor.
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	  Mod Level 5      Reference # 2.508        Date Released 09/14/84     
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	  Change: 1) Cut pin 6 of J5, pin 6 of J4 and pin 17 of J1.

	  Reason: 1) Keying of data and control cable connections.
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	  Mod Level 7      Reference # 2.859        Date Released 01/08/85     
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	  Change: 1) Replace DMA CMTRL PAL at IC37 with 502-0086-1.

	  Reason: 1) Previous PAL improperly took control of bus.
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	  Mod Level 8      Reference # 2.878        Date Released 01/11/85     
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	  Change: 1) Replace STDC ROM 1.17 at IC26 with STDC ROM 1.20
	  	     (502-0106-4).

	  Reason: 1) Allows STDC to enable or disable DMA operations on command.        -----------------------------------------------------------------------
          Mod Level 9      Reference # 3.040        Date Released 02/26/85
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	  Change: 1) Replace IC38 (PAL STDC INTTERUPT CONTROL) with 502-0123-2.

	  Reason: 1) Enable STDC to be annywhere in interrupt priority chain.
	             Previous PAL could cause bad interrupt vectors if STDC
		     was not last in the chain.
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          Mod Level 10     Reference # 3.062        Date Released 03/05/85
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	  Change: 1) Add a 330 ohm resistor from the upper pad of C7 to IC19-4.
	          2) Add a 330 ohm resistor from the upper pad of C8 to IC19-14.
	  Reason: 1-2) Increase reliabilty of VC0 circuit.