Caple C871i Bedienungsanleitung PDF herunterladen (Seite 149)

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Apple II Computer Info

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From: [email protected] (David Wilson)

Newsgroups: comp.sys.apple2

Subject: Re: II+ vs IIe Char Gen PROMs and Shift-key mods-- LC $F8 PROM mod

Date: 9 Apr 99 02:54:01 GMT

Organization: University of Wollongong, Australia

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Rubywand <[email protected]> writes:

>David Wilson writes ...

>>The only problem with this change is that the ROMs in a ][ or ][+ are not

>>pin-compatible with EPROMs of the same size. Thus, to make this change you

>>would need to wire an adapter between the EPROM and the ROM socket to sort out

>>the chip select polarities.

> True. The 2516 and 2716 2k x 8 PROMs come close.

> One problem is that the ROMs have three enable/select pins; the PROM has two.

> Fortunately, the Apple II uses only two select lines; so, the main thing you

>need to add to an adaptor is an inverter-- like a 74LS04 or any other inverting

>gate.

Acording to Jim Sather, the inverter can be dispensed with:

Pin # ROM socket 2716 (except TMS2716 - use TMS2516 instead)

18 CS2 (active high) /CE (active low)

20 CS1' (active low) /G (active low)

21 CS3' (active low) Vpp (25v prog, 5v read)

So if pin 18 (ROM) goes to pin 21 (EPROM) and pin 20 (ROM) goes to both

pin 20 and 18 (EPROM) it should work.

Looking at the 2716 data sheets I have this is not valid as Vpp is only

Apple II Computer Technical Information : Apple II Family Hardware Info

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