Re: about the plus4

From: Gerrit Heitsch <>
Date: Fri, 20 Apr 2012 19:03:15 +0200
Message-ID: <>
On 04/20/2012 06:26 PM, Ethan Dicks wrote:
> On Fri, Apr 20, 2012 at 12:11 PM, Gerrit Heitsch
> <>  wrote:

>> Using the 4164 DRAM also meant that you didn't need the extra voltages. OK,
>> the VIC and SID needed +12V like the 4116, but at least you didn't have to
>> deal with -5V for the 4116. Ask ZX spectrum owners how much headaches the
>> 4116 and their support circuits can cause.
> Dynamic PETs used 4116s, as did a number of 64K expansion boards (CBM
> and 3rd party).  I don't recall any specific problems with the -5V
> supply circuit
> in the PET, but they did have this honking-big transformer and a tap to run
> the negative supply (and just a simple LM7905 + caps regulator circuit).

Yes... That's a little different from the C64 supply or a single 9V DC 
supply as in the spectrum. Generating -5V in that environment usually 
means a little DC/DC converter which can be a pain, especially if it fails.

> What would have been an issue is a compact design with space taken up
> by a pad of 32 4116 chips compared to the space taken up by 8 4164s.  In
> the early days, 64Kbit DRAMs were not cheaper than four 16Kbit DRAMs,
> but the line on the graph was clearly heading in the right direction, and the
> amount of real estate was clearly a win from day one.

That was another reason... Later they went to the 4464 DRAMs with the 
250466 and later which saved even more space. Luckily, the VIC designers 
thought about making the refresh counter in the VIC 8Bit and not a 7Bit 
(which would have been enough for the 4164). This even allowed for some 
fun with 41256 DRAMs which only need 8Bit refresh but gave you 256KB in 
the C64 with some extra logik and software.


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Received on 2012-04-20 18:00:06

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