I found some useful information from assuearcade.com. It seems there are
some EPROM parts that would work as a replacement for the NEC PC-8300
system masked ROM.
- - - - - - -
Compatible EPROMS: NEC 27C1000 & HN27C301G. Those are the ONLY chips you
can use. They are 32 pin 1M EPROMs but are pin compatible with 28 pin 1M
uPD231000 mask ROM. All you need to do is join a wire from pin 30 to pin 32
for VCC. The top 4 pins will just hang out of the socket, don't worry about
them.
MASKED ROM EPROM
(1M) 128k x 8 mask rom (TC531000) (1M) 128k x 8 EPROM (HN27C301)
(23C1000) (NEC 27C1000)
Vpp +-v-+ 32 Vcc \
OE 2 | | 31 PGM/ | <-- Wire
pin 32 to 30 for Vcc to be on pin 28 of socket
A15 1 +-v-+ 28 VCC A15 3 | | 30 nc /
A12 2 | | 27 A14 A12 4 | | 29 A14
A7 3 | | 26 A13 A7 5 | | 28 A13
A6 4 | | 25 A8 A6 6 | | 27 A8
A5 5 | | 24 A9 A5 7 | | 26 A9
A4 6 | | 23 A11 A4 8 | | 25 A11
A3 7 | | 22 A16 A3 9 | | 24 A16
A2 8 | | 21 A10 A2 10 | | 23 A10
A1 9 | | 20 CE/ A1 11 | | 22 CE/
A0 10 | | 19 D7 A0 12 | | 21 D7
D0 11 | | 18 D6 D0 13 | | 20 D6
D1 12 | | 17 D5 D1 14 | | 19 D5
D2 13 | | 16 D4 D2 15 | | 18 D4
GND 14 +---+ 15 D3 GND 16 +---+ 17 D3
I suppose using an adapter board would look cleaner, but honestly having a
few pins hanging off the socket may not be that big of a deal..
Anyway, sorry for all the spam from me today. I got a bit excited! ;-)
Gary
On Tue, Jul 4, 2017 at 4:01 PM, Gary Weber <[email protected]> wrote:
> I keep trying to attach photos to this post thinking I can make them small
> enough. I *swear* I keep saving them as a 57k JPG but when I upload it,
> they're 200k and get rejected. Okay, let's try this a different way! Just
> embedded links this time...
>
> Okay, here's what I found in the NEC PC-8300 Technical Reference, and
> right there in plain sight, all is revealed:
> http://i133.photobucket.com/albums/q53/gweber68/NEC_PC-
> 8300_ROM_Bank_Select_zpsfnltzdo7.jpg
>
> The 128k mask PROM is the NEC uPD23C1000A. And here's the datasheet on
> the part itself: http://www.datasheet4u.com/datasheet-pdf/NECElectronics/
> UPD23C1000A/pdf.php?id=539613
>
> Seems putting a new NEC PC-8300 ROM together might be within reach, for
> those so inclined. :)
>
> Gary
>
> On Sun, Feb 19, 2017 at 1:12 PM, Stephen Adolph <[email protected]>
> wrote:
>
>> yah, thx. I think it needs to be buzzed out a bit to confirm the
>> actual pinout...
>>
>> On Sun, Feb 19, 2017 at 12:20 PM, Kurt McCullum <[email protected]>
>> wrote:
>> > Steve,
>> >
>> > Keep in mind that I am guessing on the PROM based on the limited number
>> of 128k 28 pin PROMs available at that time. That's a pinout for the NEC
>> PROM but I don't know if that is the actual part which was used. There
>> should be a number on the chip that may lead to the answer.
>> >
>> > Kurt
>> >
>> > -----Original Message-----
>> > From: M100 [mailto:[email protected]] On Behalf Of
>> Stephen Adolph
>> > Sent: Sunday, February 19, 2017 5:13 AM
>> > To: Model 100 Discussion <[email protected]>
>> > Subject: Re: [M100] Parts for an NEC PC-8300
>> >
>> > .. comparing a 27C1001 pinout to the one from Kurt, it looks like it
>> may just be possible to stuff a 27C1001 and wire up only a couple of
>> signals.
>> >
>> >
>> > On Sat, Feb 18, 2017 at 8:12 PM, Stephen Adolph <[email protected]>
>> wrote:
>> >> come to think of it, you could probably tie /CE and /OE together.
>> >>
>> >> On Sat, Feb 18, 2017 at 8:08 PM, Stephen Adolph <[email protected]>
>> wrote:
>> >>> I did not grasp how much information is in that 500MB tech reference
>> >>> doc for the 8300. Wow!
>> >>>
>> >>> probably the best documented Model T.
>> >>>
>> >>> It is clear that the ROM is 128KB, and I think it is also clear that
>> >>> without some custom solution, one can't make a replacement main rom
>> >>> for the 8300 easily. At best you might be able to program a 27C1001,
>> >>> and then do a custom adapter board.
>> >>>
>> >>> A normal eeprom needs both a chip select and an output enable, so
>> >>> some extra logic might be needed too.
>> >
>>
>
>
