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Nslu2 RS232 – Adding serial connector

Adding a serial port to our nslu2 is very easy. You can solder a Male or a Female DB9 serial connector, remember, if you use a male connector (such a normal pc) you can plug any kind of serial device and you it as a console port (with a correct cable); if you use a female connector you can plug that port directly into another computer and use only as console.

NSLU2 has one serial port with TTL signal-level (3.3V), for more information read this.

I don’t want to see anything outside the nslu2 (only the connector itself) so i’ve looked for a microchip that doesn’t need anything else than RX-TX and power supply.

So i found MAX3233 (datasheet), it’s fantastic! You need only one 0.1uF capacitor for spurious power supply (really, i don’t use it 😉 ).

Here is the tipical schematic of MAX3233 from

As you can see we can have up to two serial port, and no need of external capacitor.

Starting opening our nslu2 and looking near battery. You can see four unused hole, this one is RS232 pins (looking image 1).

The first one (near battery) is 3.3 V, the second one is RX, third is TX and fourth is GND. Take 4 piece of cable and:

– connect pin 1 of nslu2 to pins 5-9-10 of MAX3233;

– pin 2 with pin 1 of MAX3233;

– pin 3 with pin 3 of MAX3233;

– pin 4 with pin 18 of MAX3233;

Now you can solder also the serial connector, pin 5 is ground so connect it with pin 18 of MAX3233.

Assuming that you are using a male connector you have to solder pin 3 of DB9 with pin 19 of MAX3233 and pin 2 of DB9 to pin 20 of MAX3233. If you use a female connector (only for console) simply invert pins 2 and 3 onto DB9 connector.

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