Add a Serial port to the LS MINI
- 1 Background
- 2 Method
- 2.1 C54
- 2.2 Pinout of Port
- 2.3 Use a Level Shifter
- 3 Serial Port Output
- 4 References
Apparently there are two traces that have been interrupted which would allow serial port access.
These traces have been interrupted UNDER a SMD capacitor at position C54. Junker (see Yamasita's article/reference) discovered the way first. Apparantly the pinheaders from the SCON-KIT/ PRO can be fit into the case quite easily as well.
We need to fix these wires which go under C54:
Method 1: reconstruct the traces (on the backside)
This method requires absolutely no soldering.
Lay a layer of a scotch tape between holes, just not to cover them.
Use a strand of high flexible low oxygen copper wire.
- thread it through both holes,
- fix it with a scotch tape on the back side and then
- cut remainders on the front side, leaving about 2 mm.
- repeat with the second thread.
Be sure not to shorten anything else.
Method 2: Bridge the traces (on the frontside)
This method requires a steady hand and good soldering skills.
Use two strands of high flexible low oxygen copper wire.
- Locate and carefully remove C54 from its pads.
- Clean the area with rubbing alcohol and a tiny brush.
- Cut two stands of high flexible copper wire to length.
- Solder each of the strands to the vertically aligned pads.
- Resolder C54 to its' original position.
- Ensure no shorting has take place while soldering.
Pinout of Port
Use a Level Shifter
The serial port signals from the processor are only 3.3V. For proper RS-232 12V signaling, an RS-232 level shifter needs to be added. These are very common in PDA serial cables also, but can be purchased
Build your own LVTTL/RS232 or LVTTL/USB interface
- LVTTL/RS232 - Building a Custom Serial Interface
- LVTTL/USB - Use a Nokia Serial Cable on an ARM9 Linkstation
- LVTTL/USB - Use a cheap phone sync cable with the serial port
Buy your own TTL Level Shifter
- LVTTL/RS232 - MAX232 based from Futurelec - MINIRS2323V
- LVTTL/USB - FTDI chip based cable - TTL-232R-3V3
Usage considerations for the TTL-232R-3V3
A working/tested pinout/wire-color scheme is:
- Solder the 4-pin header to the board. Make sure you don't have shorts.
- You will need to switch wires on the TTL-232R-3V3 cable. Use a sharp object to lift the plastic tabs and carefully pull the wires out. Rearrange them according to the table above (black, empty, orange, yellow, empty, empty) and slide those wires back in. Tape the other wires to make sure they don't short anything.
- When plugging in the cable, make sure black aligns with GND, yellow with TXD, and orange with RXD.
- Connect the USB cable to your computer, start a terminal program with the right settings.
- Turn on the device, you should see output from the bootloader in couple seconds.