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Serial Port HW on Linksys WRT54G3G
15 October 2009 - 6:56pm
There is a header behind the front panel.
The header has the serial port signals, but they are 3.3V and no handshake. A real serial port is +12V and -12V signals.
If you add an RS232 9 pin interface you will by default get the Console. To do anything useful you need to install the OpenWRT Software (White Russian recommended for older WRT54G3G)
| Pin | Signal | Colour | Pad |
|---|---|---|---|
| 1 | +3.3V | ||
| 2 | TXD | P4 | |
| 3 | RXD | P3 | |
| 4 | NC | ||
| 5 | GND | P1 |
Cut the top edge of the plastic front for the 9 pin D-Connector.
You need a MAX 232 type IC to convert the 9pin 12V PC signals to 3.3V levels.
PC Male Socket on PC case, Original Female skt on Linksys
Direction of Signal is from PC viewpoint.
| Pin | PC Signal | PC In/Out | Converter | Description |
|---|---|---|---|---|
| 1 | DCD | In | Pad | Data Carrier Detect (Not used) |
| 2 | RxD | In | IC1 (14) Out | Receive Data |
| 3 | TxD | Out | IC1 (13) In | Transmit Data |
| 4 | DTR | Out | jp1b, D1 | Data Terminal Ready (+12V ) |
| 5 | GND | - | IC1 (15) | Ground |
| 6 | DSR | In | jp1a | Data Set Ready (Not used) |
| 7 | RTS | Out | Pad | Request To Send (+12V) |
| 8 | CTS | In | IC1 (7) | Clear To Send (Not Used) |
| 9 | RI | In | Ring Indicator (Not Used) |
To simulate handshake and/or make Windows happy:
Tie Pins:
1) DCD, DSR to DTR
2) CTS to RTS
Pin numbers straight to same number on Linksys Female socket.
Use a Male to Female (i.e. extension straight through cable) 9 pin cable.
If using the module from a Nokia PopPort Serial Connector/Adaptor
Remove D1, D2. Connect 9V to 12V to D1,D2 pads furthest from connector via 180R. It must be powered internally, not from connected device.
Cut track at pin 8. Short pin 7 & 8 (CTS & RTS).
Short JP1 and Pin 1 (DCD, DSR & DTR).
For Reference: PC 25Way Serial Port
PC 25 Way on PC case. The Modem has the same signals but the direction is reverse, thus a one to one
STRAIGHT cable connects to modem [ x] are 9 pin numbers, thus numbers for 9pin female to 25 pin male Modem
cable
| 25 Pin (9) | Name | PC--Ext | Description |
|---|---|---|---|
| 1 | SHIELD | Shield Ground | |
| 2 (3) | TXD | --> | Transmit Data |
| 3 (2) | RXD | <-- | Receive Data |
| 4 (7) | RTS | --> | Request to Send |
| 5 (8) | CTS | <-- | Clear to Send |
| 6 (6) | DSR | <-- | Data Set Ready |
| 7 (5) | GND | == | System Ground |
| 8 (1) | CD | <-- | Carrier Detect |
| 9 | n/c | ||
| 10 | n/c | ||
| 11 | n/c | ||
| 12 | n/c | ||
| 13 | n/c | ||
| 14 | n/c | ||
| 15 | n/c | ||
| 16 | n/c | ||
| 17 | n/c | ||
| 18 | n/c | ||
| 19 | n/c | ||
| 20 (4) | DTR | --> | Data Terminal Ready |
| 21 | n/c | ||
| 22 (9) | RI | <-- | Ring Indicator |
| 23 | n/c | ||
| 24 | n/c | ||
| 25 | n/c |
