Building a Dreamcast Serial Cable with a Max233
===============================================

This is pretty much identical to what I did with the Nokia cable 
(http://www.harmlesslion.com/stuff), and, pleasantly, it works. ;)

WARNINGWARNINGWARNING - DANGER, Will Robinson! 

This is WRONG. This is NOT the right way to do it. This is the 
stupid lazy way to do it. If it doesn't blow up your Dreamcast 
it will drastically shorten it's life (or at least that of the 
serial port). If, however, you're like me, you have Max232/233s 
laying around and don't wanna wait to find/order/get a Max3222, 
then this works. For me, anyway. Note that I'm not all that great 
with electronics, and this is almost verbatim the standard Max23x 
circuit right out of the data sheets, which you should get from 
Maxim's web page (www.maxim-ic.com) if you want to work with this 
stuff. There are modifications you could do to make the voltage 
flowing into the DC a little friendlier, but I don't know how to 
do them, and this works. ;)

Ok. You need:

-Max233 or Max232 IC. (The 233 does not require the external 
 capacitors to form the power supply)
-Maxim RS232 transceiver Data Sheet 
 (http://pdfserv.maxim-ic.com/arpdf/1798.pdf)
-1 - 1uf, 16v capacitor  (for Max233)	 or
 5 - 1uf, 16v capcitor (for Max232)
 (and if you want to try another Max chip, follow the datasheet...)
-Serial cable for your serial port (9 pin assumed here)
-Cable for the Dreamcast Serial port, however you want to get it ;)

The Maxim Rs232 Driver/Receiver ICs are really very cool chips. But 
all they do is convert between TTL/CMOS, and RS232 levels. TTL runs 
between 0 and +5v, while RS232 runs from -5v to +12v (as I 
remember... might be off.)

Anyway, the Dreamcast runs at 0 and +3v, so the signals need to 
be converted. If you check the datasheets, you'll see that the 
Maxim chips have two lines running in each direction, labeled 
T1, T2, R1 and R2 (TTL 1, TTL 2, RS232 1, RS232 2). So all we 
have to do is hook everything up.

Disclaimer: I haven't build the 232 version, but the chips are 
identical and it should work just as well. Also, I'm using a 
North American Dreamcast, model HKT-3020.

		MAX233					MAX232
	T2in	*	R2out			C1+	*	Vcc
	T1in		R2in			V+		Gnd
	R1out		T2out			C1-		T1out
	R1in		V-			C2+		R1in
	T1out		C2-			C2-		R1out
	Gnd		C2+			V-		T1in
	Vcc		V+			T2out		T2in
	C1+		C1-			R2in		R2out
	Gnd		V-
	C2-		C2+
  
	(note: the datasheet incorrectly
	labels C2- as "CS-")

Note the Max233 is 20 pins, while the 232 is only 16 pins.

	PC Serial, 9 Pins, Male			Dreamcast Serial, 10 pins, female
	
	1 2 3 4 5				1 2 3 4 5 6 7 8 9 10	
	 6 7 8 9				(viewing from the back)

	1 - Carrier Detect			1 - +5v
	2 - RXD					2 - ?
	3 - TXD					3 - Gnd
	4 - DTR					4 - RXD
	5 - Gnd					5 - TXD
	6 - DSR					6 - RTS
	7 - RTS					7 - CTS
	8 - CTS					8 - ?
	9 - RI					9 - ?
						10- +3.3v

I'll list the connections by name here, you can draw it up and work 
out which wire goes where ;)

Max232:
Connect C1+ to C1- through a capacitor
Connect C2+ to C2- through a capacitor
Connect V- to ground through a capacitor
Connect V+ to Vcc through a capacitor
Connect Vcc to ground through a capacitor

Max233:
Connect the two ground pins together (with a jumper wire)
Connect the two C2- pins together
Connect the two C2+ pins together
Connect the two V- pins together
Connect Vcc to ground through the capacitor
Do not hook anything up to C1+, C1- or V+

Both:
Connect Dreamcast ground to ground
Connect Dreamcast RXD to Max R2out
Connect Dreamcast TXD to Max T2in
Connect Dreamcast RTS to Max T1in
Connect Dreamcast CTS to Max R1out

Connect PC RXD to Max T2out
Connect PC TXD to Max R2in
Connect PC DTR to Max Vcc
Connect PC ground to ground
Connect PC RTS to Max R1in
Connect PC CTS to Max T1out
Do not hook up PC CD, DSR or RI.

Testing: 
You can test the basics before hooking up to the Dreamcast. Plug in 
to the PC serial port, open a terminal program, and type a few 
characters to turn it on. If you check the voltage at VCC, it should be 
4-5v. (The PCs DTR is used to power the circuit). If you check the 
voltage at V+, it should be around 10v. And if you check V-, it should 
be around -10v. This tells you the power supply is working.

On the Dreamcast end of the cable, if you connect RTS to CTS, and RXD 
to TXD, you should be able to type characters in the terminal program, 
and see them echoed back. This tells you that the chip is correctly 
converting from RS232 to TTL, and back.

Now you can hook it to the Dreamcast, boot the serial CD, and there 
you go. ;) You will want to set 57600 baud, 8N1, local echo, RTS/CTS 
flow control, and make sure enter sends CR/LF, just CR doesn't 
work. (For me, anyway). 

No idea what to type? Try:
>S70500000000FA

heehee....

Sources:
REAL Serial cable schematics, docs, and serial slave CD: http://marcus.mangakai.org/dc
Maxim IC documentation: http://maxim-ic.com
Nokia circuit using Max232: http://www.hut.fi/~ptuomine/nokia/cables/fbus.htm

							-Tursi (M.Brent)
							http://www.harmlesslion.com

(oh, that mysterious string to type tells the Dreamcast to cold boot, that's all ;) )

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