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bobbydilley

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Hello,

Does anyone know anything about the Sega Naomi RS422 port on the front.

I'm trying to setup a Derby Owners Club system, and want to be able to use the RS422 on the front for the card reader emulator.

I have attached it to an RS422/485 to USB converter, and I get data, but it is all 0s.

I'm aware that the Derby OC system uses some sort of RS422 to RS232 converter, so I'm wondering if this is actually non standard RS422? Does anyone know of any other Naomi 1 games that use the RS422?

Thanks,
Bobby
 

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What does your jumper look like on the mainboard where you insert the cart
 

bobbydilley

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I’m assuming you’re talking about the jumpers for the RS232 vs RS422 communications. Those jumpers are only present on the later Naomi 1 consoles, and the Naomi 2s.

I have an early revision Naomi 1 that doesn’t have those jumpers, and can only output RS422.

Thanks for the suggestion though!
 

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Miss the Naomi 1 part. Hope you find a solution
 

stj

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i dont know if it's the same on naomi 1 and 2, but i traced all that crap out some years back and you can switch the serial from rs232 to rs422 using the jumpers.

if somebody wants to host upto 5 gigs of data or knows a reliable free hosting platform, i have literally a couple of decades of roms, manuals, schems, notes, mods etc i collected and in some cases drew up.

including usefull little things like monochrome to rgb converters on stripboard - for putting pre-1980 stuff onto jamma adapters or just using modern(ish) monitors on old cabs
 

rtw

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I have some spare space, feel free to PM me 😀
 
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stj

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nice - i'll start getting it together from several drives :)
incidentally, some of it is romdumps from before mame - when i helped dave spicer with "sparcade"!!!!
 
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rtw

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Sparcade haven't heard that name in a while :D

sparcade.png
 
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bobbydilley

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nice - i'll start getting it together from several drives :)
incidentally, some of it is romdumps from before mame - when i helped dave spicer with "sparcade"!!!!
Funnily enough my dad used to be friends with & work with Dave Spicer. I remember him telling me about Dave's Starwars machines, and trying to run Sparcade when I was about 10. Small world.

> i dont know if it's the same on naomi 1 and 2, but i traced all that crap out some years back and you can switch the serial from rs232 to rs422 using the jumpers.

So we're clear on this bit - you CAN switch what is output from the front of the Naomi (Naomi 1 CRX & Naomi 2) with the jumpers, however it is NOT a pure transparent protocol conversion. The RS232 and RS422 lines are on two completely different busses inside the Naomi. The Naomi game would have to specifically decide which bus to send the data down, and so even though you can move the jumpers the game is going to be sending data to either RS422 or RS232.

However, we do have some resonably good news I think. I've done a logic analyzer dump on the protocol sent from the RS422. It is attached here, and can be viewed using Logic 1 by Saleae which you can download here: https://support.saleae.com/logic-so...er-software-releases#logic-1-x-download-links.

Still finding it difficult to work out exactly what the baud rate / stopbits / databits etc. are - but I'll report back when I have concluded!
 

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bobbydilley

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Turns out I was undersampling it quite badly, so the "guess" feature got angry!

Will re-do with a higher sample rate, and hopefully it'll be able to tell us!
 

bobbydilley

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1651589499828.png

1651589777106.png


2Mbps with 20 bits per word :S

Either my analyzer can't cope with the signal, or it's the strangest protocol ever.
 

bobbydilley

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It was very slightly wrong, it's still a weird protocol though. RedOne has managed to use a proper scope to record it, and the conclusion is this.

1651654536957.png


It is running at 2Mbps

It is actually 1 start bit, 8 data bits, 1 stop bit - but sent twice in quick succession, leading me to think it was 20 bits.

Looks like my RS422 to USB convertor can run at a maximum baud of 3Mbps, so hopefully 2 should be fine!
 
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bobbydilley

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```
b'\x01', b'\x02', b'\x01', b'\x07', b'\x01', b'\x10', b'\x01', b'\x00', b'\x01', b'\x00', b'\x01', b'\x00', b'\x01', b'0', b'\x01', b'\x03', b'\x01', b'$'
b'\x01', b'\x02', b'\x01', b'\x07', b'\x01', b'\x10', b'\x01', b'\x00', b'\x01', b'\x00', b'\x01', b'\x00', b'\x01', b'0', b'\x01', b'\x03', b'\x01', b'$'
b'\x01', b'\x02', b'\x01', b'\x07', b'\x01', b'\x10', b'\x01', b'\x00', b'\x01', b'\x00', b'\x01', b'\x00', b'\x01', b'0', b'\x01', b'\x03', b'\x01', b'$'
```

And we can read it, and it's quite evident what it's doing!

The first byte is always 0x01, which you assume means that the conversion board has multiple outputs and its asking for output 1.

The second bytes are what you'd expect from the serial communications to the card reader.

0x02 Start Byte
0x07 Length
...
0x03 Stop Byte
$ Checksum

(Appologies for the strange way python writes out bytes)

Edit:

Thinking more about it, it's RS422 which is multi node just like JVS. I suspect that the first byte is the address of the item on the line (not saying that the output board couldn't be multiple nodes). You'd think that the replies probably should go to 0x00 in this case.
 
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bobbydilley

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So as a premature conclusion (as this still needs to be tested), the Naomi RS422 Derby Owners Club protocol:

baudrate 2000000
data bits 8
stop bits 1
parity bits 0

Take every 2nd byte, and send that straight to the card reader.

Now to work out how replies work :S
 
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