On 2012-06-06, at 17:45, Gerrit Heitsch 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 HIGH. I would prefer a "universal" method that would apply to all boards. I take that CS on pin 21 is active HIGH and connected to +5 all the time but the other is active LOW and needs to be pulled up if not connected. Unless it is already pulled up somewhere on the board (rather than inside PLA - I have to check it), a pull-up resistor should be added. But if there is no pullup for the line already on the board and grounding the CS1 is easier (should be) than I would of course prefer this method. I hope there are no boards' revisions that would make this difficult. -- SD! Message was sent through the cbm-hackers mailing listReceived on 2012-06-06 21:00:05
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