Date   : Fri, 10 Dec 2004 13:24:23 +0000
From   : mick@... (Mick Champion)
Subject: Eprom Programmer 

To the BBC list, 
 
Sprow wrote : 
Sprow> 27128 - NMOS, 21V for Vpp 
Sprow> 27128A - NMOS, 12.5V for Vpp 
Sprow> 27C128 - CMOS, far too weedy to drive the bus 
 
I have had 3 working 27C128s installed in my model B for two years now. All 
were programmed using a programmer that I built using Angus's superb design, 
so it is possible. The 20k resistor on the TL497A had to be changed to 15K to 
reduce the programming voltage to 13v. The resulting heat reduction inside the
BBC is great as C128s hardly get warm. 
 
 
There was a also a mistake in the 1985 version of EPROG.PDF. The correct 
wiring, is for both 5Ds on the two 74LS374's to be strapped to PB4, and both 
6Ds to PB5. On my PDF version, the right hand 74LS374, shows 'incorrectly' 
that 5D goes to PB5 and 6D to PB4. The PDF may have been updated by now, 
ignore if it has. 
 
 
Mick. 
  
 
 

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