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This page describes how to build an
adaptor for the Dreamcast serial port that will allow
you to connect it to any computer using a standard 9-pin
DSUB connector. The main component is a MAX voltage
converter, since the Dreamcast serial port uses CMOS
(3.3V) voltage levels, whereas normal RS232 uses +/-12V
levels. If you are having trouble finding the MAX chip,
you may want to consider ordering it direct lt from
MAXIM, or failing that from ELFA (stock no. 73-228-45).
Dominic Clifton informs me that UK residents can get the
chip from RS Electronics (+44 01536 201201), where it
has a part number of 1891469.
Notice: Cables that are functionally
equivalent of the one described here can now be bought
from Lik Sang, saving the trouble of building one
yourself. The product is called "DC Coders Cable".
This serial adaptor has been designed,
built and tested by me. It works perfectly for me, but I
will not be held responsible if it fries your DC, your
computer, and/or your hair. Also, please note that you
will probably only find this interface usable if you're
writing and running your own software for the DC. I
don't know of any "standard" software that communicates
anything of interest to a computer on the serial port.
Here's what you need:
One DC<->NeoGeo link cable (you can get
it at Neo Geo Pocket Store, David Console Shop, or
Amazon for example)
One MAX3222CPN line driver / voltage
converter
Four 0.1�F capacitors
One 9-pin DSUB connector (male)
Some bits of insulated wire
Optionally: A pair of 6-pin connectors
(DIN/whatever)
The reason I've used the DC<->NeoGeo
link cable is that it provides the right type of
connector for the DC serial port, removing the need to
solder directly on the DC. It also contains a full set
of line drivers, reducing the risk of damaging the DC if
you make a mistake. So what I did was to get the NeoGeo
link cable, and cut the NeoGeo-end in half. This leaves
a set of colored wires hanging that can easily be
soldered as needed. You can either connect the cables
directly to the MAX, or do as I did and solder on a
connector of your choice (i used a DIN6 connector),
allowing you to easily separate the voltage converter,
and reconnect the NeoGeo connector cable end should the
need arise. A third alternative is to remove the NeoGeo
cable altogether, and connect directly to the CON1
connector on the link cable circuit board. This is the
method pictured on the blueprint below, but the cable
colours are also provided, if you want to use another
option. Below is a picture of the DIN6 variant (the
thing just behind the right of the DC is a VGA box, and
not part of the serial adaptor):
Now, the first thing you have to do is
get a +3.3V feed. The CON1 connector (and therefore the
NeoGeo cable) has all the necessary signals, except the
voltage needed to drive the MAX chip. Fortunately, there
are several easily accessible locations on the NeoGeo
link cable circuit board where you can tap off the
+3.3V. Open the black box and locate the diode marked D1
(it's right in the center of the right half of the
board, surrounded by resistors and transistors). Just to
the left of this diode, there should be a small hole.
This is a through hole for the +3.3V (it passes from the
bottom side of the board to the top side). This is an
ideal spot to attach a wire, just put it thouth the hole
and solder it at the opposite side. Then make a small
hole in the side of the plastic box and you can extract
the other end of the wire. In the picture above, you can
see a thin green wire coming out of the box in this way.
Note that this wire is the reason I used 6-pin DIN
connectors, and not 5-pin.
When you have the +3.3V and the CON1
wires, all that remains is to solder everything
together. Click on the blueprint to get a PostScript
version suitable for printing.
For those of you so inclined, there is
also a PCB design available, courtesy of Mathew Boon.
Please consult the blueprint below for placement of the
capacitors.
To connect the adaptor to a computer,
you should use a crossed cable (0-modem). To connect a
modem (no idea why you should want to do that, but
hey... :) use a straight cable. The adaptor has RTS/CTS,
so you can use hardware handshaking. The MAX3222CPN is
guaranteed to handle bitrates up to 120kbps. |
