I tried posting this 2 time and did not show up, trying a 3rd time....
A quick google search for 831000 Mask ROM, the first link I find this exact
comparison
Not my work, I just copied and pasted text, hopefully show up readable.
Showing how pins of a 27C1000 line up perfectly as a substitite for a 831000
and a guide to what the pinout of the PC8300 ROM 0 socket must be
531000/831000 27c301/27c1000
Vpp 1 +-v-+ 32 Vcc
OE 2 | | 31 PGM/
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
The UV EPROM I used was an ST brand , M27C1000-20F1
Kyle
--- On Thu, 3/2/17, kyle jenne <jenf...@yahoo.com> wrote:
> From: kyle jenne <jenf...@yahoo.com>
> Subject: Parts for an NEC PC-8300
> To: m100@lists.bitchin100.com
> Date: Thursday, March 2, 2017, 7:42 PM
> I had this same question a few years
> back.
> I have not been tinkering with my 8201s or 8300 for a while,
> but stored away.
> But I found some notes.
> I had found out that the NEC-8300 system ROM is
> an 831000 128k x 8bit Mask ROM 28 Pin (the single chip
> labeled 831000-438 , N83A Basic ...) in socket ROM 0
> I have an 8300 with the correct original system ROM.
> I remember figuring out how to read this ROM and verified it
> is the same image you do find in VirtualT.
> I also aquired 1 of those 8300s with a custom operating
> system for some kind of
> factory or Lab testing? It had a common 27C256 for a system
> ROM 0 which led me to believe
> it is safe to use a 27C256 in ROM 0 socket obviously.
> I found that an original 8201 system ROM or a 27C256 burned
> with the 8201 system ROM
> seemed to work fine in this 8300.
> No extensive testing but I never saw an issue. It just
> functions like an 8201 obviously.
>
> For a 8300 ROM replacement I had found that an ST
> M27C1000 128K x 8 bit 32 Pin UV EPROM
> would be the best/easiest replacement for the
> original.
> No real adapter needed if I figured correctly. No cutting
> pins or rerouting pins necessary.
>
> Somewhere I'm sure I found and confirmed the correct pinout
> of an 831000 mask ROM as a pinout guide.
> A 27C1000 plugs right into the ROM 0 28 Pin socket,
> I believe I just straight burned the VirtualT 8300 system
> ROM image to the 27C1000. No tricks.
> Insert correct orientation in ROM 0 leaving Pins 1&2 and
> 31&32 of the
> 27C1000 hanging out in mid air. (bottom edge of the
> computer)
> I soldered a small wire connecting overhanging not connected
> pins
> 1&2 (VPP and /OE I believe) together and to Pin 16
> (GND)
> On the other side I soldered overhanging not connected Pins
> 31&32
> (/PGM & VCC) together and to pin 30 (NC) to pick up VCC
> from the socket below (ie 30&31&32 together)
> All of this on the 27C1000 EPROM itself, no mods to the
> computer and no damage to the EPROM either.
>
> This worked and acted like an 8300. Switched to 8201 mode
> with the OUT command. etc.
> No extensive testing, but seemed to work fine.
> Then I put my 8201s and 8300s away awile ago. But found some
> of my notes.
> I only had the 1 27C1000 scrounged from an old computer when
> I figured out what I needed
> so I don't have any more.
> I remenber other similar 128K x 8bit UV EPROMS 27C1001 ? and
> such didn't have
> the pinout that matched up perfectly like the ST
> 27C1000-20F1 I was luck to have.
> Don't know if that is the right speed IC but it seemed to
> work.
>
> Hope this is helpful, again some info is from memory
>
> Kyle
>
