Re: 6502/6510 ROM selection daughterboard

From: Gerrit Heitsch <>
Date: Wed, 06 Jun 2012 17:45:31 +0200
Message-ID: <>
On 06/06/2012 01:18 PM, wrote:
> On 2012-06-06, at 04:35, Jim Brain wrote:
>>> If it is enough to grab that one line (after Gerrit's e-mail I got
>>> enlightened ;-) than I'd leave the original ROM where it is
>>> (especially if not socketed) and tap only on the line either by
>>> cutting a trace or unsocketing a pin from PLA. I believe it is better
>>> to let also people with soldered-in ROMs do it without unnecessary
>>> desoldering. Of course if someone has it socketed and wants to save
>>> some milliamps - sure. But I would prefer not to _require_ removing
>>> the chip.
>> Not removing the IC means you need to "disable" it somehow.
> By redirecting _CS from it to the board?

You can leave the trace between the PLA and the Char-ROM in place. The 
Char-ROM is a 2332 which has 2 _CS signals, one of them active HIGH in 
this case. All you need to disable the onboard Char-ROM is to cut the 
connection between pin 21 and pin 24 and then tie pin 21 to GND. On some 
board revisions this is easily done (250466 for example), on others 
cutting the trace between the PLA and the ROM might be easier. In that 
case you have to connect pin 20 to pin 24 using a pullup resistor (4.7 
KOhm schould do) since open inputs are usually but not always considered 


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Received on 2012-06-06 16:00:06

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