Wrt54g - ByteWiki

Oh so sweet! I just got one of these routers and it's gunna be tough not to put it under the knife.

Like all WRT54G, the version 3.1 has 8 GPIO pins.
PIN Usage Comments
0 Unknown Not WLAN like other versions
1 Power LED 0 = Flashing 1 = On
2 White LED 0 = On 1 = Off
3 Orange LED 0 = On 1 = Off (Or better, set to input)
4 Cisco Button Pressed/Grounded = 0, Break = 1
5 Unknown ADM_EEDI/robo_reset
6 Reset Button Pressed/Grounded = 0, Break = 1
7 DNZ LED 0 = On 1 = Off

The GPIO pins run of 3.3 volts so it is handy to have a 3.3 volt power source. There are a few places you can get power from the WRT54G. At first I used the serial port pins 1 & 10, but then I neede to attach a serial port so I switched to the JTAG plug. JTAG howerver does NOT supply power, so that did not work and I switched back to the serial port. I recommend that you solder in the header pins on top, and then take power from that. If however you want to run serial as well, you can solder onto the underside of you header pins. You can solder directly onto the board, but it becomes a pain if you want to remove them and attach a serial port.

Wrt54g - ByteWiki