GPIO lines can be used to connect devices to the WGT634U, using SPI or I2C protocols, or just to light an LED or listen to a button. People have added SD card readers to WRT54Gs this way.
[http://kiel.kool.dk]
[http://forum.openwrt.org/viewtopic.php?pid=33727] .
I poked at the hardware with CFE:
CFE> d b8000060 10
B8000060: 000000FD 000000FD 000000C3 00000000 ................
CFE> e b8000064
Type '.' to exit, '-' to back up, '=' to dump memory.
B8000064: [000000FD]: ff
B8000068: [000000C3]: ff
B800006C: [00000000]: .
CFE> d b8000060 10
B8000060: 000000FF 000000FF 000000FF 00000000 ................
CFE> e b8000064
B8000064: [000000FF]: 00
B8000068: [000000FF]: .
CFE> d b8000060 10
B8000060: 00000000 00000000 000000FF 00000000 ................
CFE>
The four sequential words are
- 0xb8000060: input
- 0xb8000064: output
- 0xb8000068: output enable
- 0xb800006c: control (seems that zero activates the I/O line)
In the sequence above I set the 8 GPIO bits to output mode and commanded them to 1's (+3.3V logic level). Then I set them all to 0's.
With a meter I identified 7 of the eight bits:
0x80 | TP1 |
0x40 | TP2 |
0x20 | TP3 |
0x10 | TP4 |
0x08 | U6.13 to yellow Poer LED |
0x04 | reset pushbutton on back panel |
0x02 | TP5 |
0x01 | unknown |
The testpoints TP1 - TP5 are little gold pads near the Broadcom chip.
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