PSOne USB Link (Serial)

This is one of the first mods I did to a PSone, other than a modchip of course.

This was inspired by a post by Defor on Assemblergames who was discussing how feasable it would be to fit a link port to a PSone, which obviously doesnt have one as standard. He had traced out the SIO lines from the CPU. You can find these by looking at the the service manuals for the PSone..


Work in progress….


Crude schematic..


The 74HC244 buffers the FTDI from the CPU when the unit is powered down, preventing random garbage going either way when the PSone isn’t in use. You could probably power the FTDI from a 3.3v source on the PSone side which would achieve the same thing.

Work in progress….


Lid back on….


So now you ask how do you use it? Firstly you will need the patched Yaroze boot CD that is kicking around on the internet. Secondly you will need the Yaroze compiler and tools (also google will serve you well on this). And an emulation environment such as DOSBox. DOSbox works well and I set up the Yaroze compiler within that. Edit dosbox.conf by adding a realport line  for serial1 matching the COM port of your FTDI’s virtual com port. It works absolutely fine all the way up to 115,200bps. Example below :-


# Possible values: dummy, disabled, modem, nullmodem, directserial.

serial1=directserial realport:com12

Example batch file to set up the yaroze compiler etc..

@echo off
ECHO ================= SONY NET YAROZE ENVIRONMENT ================
set DJGPP=c:/psx/djgpp.env
PATH %path%;c:\psx\bin;c:\psx\gnu\bin
set TMP=c:\tmp
set DTLH3000=0x3f8,4,115200


And there you have it, play around with yaroze stuff on a smaller machine, at a fraction of the cost and no legacy hardware required.

8 thoughts on “PSOne USB Link (Serial)

  1. You obviously know what you’re doing matey (directed here by a nice chap on the PSXDEV boards) – How easy would it be to take this idea to replicate the link functionality? Purely would like to get my 2 PSones talking for some old school link up gaming 🙂

    I don’t suppose its as simple as wiring an ethernet port straight to the right pins is it?

    • Easy to do, just wire them up across in a null modem fashion ( rxd-txd, rts-cts etc.). If you mean ethernet there is no way to network them easily using the internet afaik. Different games use different protocols and baud rates.

      To link two together you could use Ethernet ports and cables for simplicity as you only need 7 wires, but obviously this would not give you an Ethernet connectio, you would just be using Ethernet cable and RJ45 connectors

    • I have tried this with a few devices with no success.. I have tried HC-05/06 devices and preconfigured them for 115.2k but the software doesnt actually execute the code. I am currently working on using an ESP-8266 as a WiFi-UART bridge and writing a Python client for it. Watch this space.

    • Wouldn’t say better at all, but definitely another option.

      I have tried this with some HC06/05 modules (iirc) and none of them worked with the standard psxserial client at the time. It would say recieving data but never executed.

      I may revisit this in the future if anyone is interested.

  2. HI man, i cant understand your work, but i sure woud like to ask someone to try linking 2 PSOnes. Can you post a tutorial for that please?

    • I wouldn’t cover that here, but if you wanted to do that just literally connect them together but with the lines switched around in a “null modem” type fashion… RXD-TXD,TXD-RXD,RTS-CTS etc.. etc. The test points are the same. A user named Defor tried this on Assemblergames and had it working.

  3. Hey Dan,
    I picked up a working PSONE (102 PM-41-51) got it for an amazing prize 40AUD!
    And wanting to turn it into a pseudo Net Yaroze, I’m trying to figure out your CPU/pad pinout image, but it’s very low res, I guess it’s not required as there’s different versions of the MB.
    Anyway, here are some of my notes so far, I hope you don’t mind me adding to your tuts 😀

    For anyone else wanting to do this: I found a good service manual with all PSONE rev MOBO’s pinouts, PDF’s here:

    Defor (from AS forum as you said) “(Pins 70-75 of the CPU on both board layouts specifically) ” which looks correct on my MB also.

    I see his PSONE image (topside) is wired the same as yours (not sure which rev MB tho)

    So I’m still figuring out which CPU pins/Pads correspond to my MB and the serial FDTI as per your Net Yaroze cable tut

    I’ll post a pic of my MB with that I think looks correct 😀

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