Setting up the serial port is very easy, since it's only 3 wires
Still many people get it wrong first. Unfortunately the doc manual caused some confusion with swapped TX/RX. Check [rs232 pinout] yourself if you like. Note that DSUB25 (that is rarely used) standard has TX-RX swapped compared to DSUB9. (DSUB=DB).
Q: Is there any way to make sure that you've connected the right pins by measuring impedance or diode voltage across the pins of the serial port ?
How to make the RS232 cable for GenBoard/VerThree
Only 3 wires are needed for the cable. Shielded cable is highly recommended in a production environment. Shield must be connected at only one side (either PC or GenBoard), so ground must have a dedicated wire inside the (min. 3 wires + shield) cable.
| DB9 | Direction | SV2 | EC18 | Earphone plug | |
| 3 | --> | 1 | EC18-pin14 | RING | Data transmitted by PC, received by genboard. |
| 2 | <-- | 2 | EC18-pin15 | TOP | Data received by PC, transmitted by genboard. |
| 5 | <-> | 3 | use GND | Base | You can use a GND pin (but NOT GND5: the power-GND would insert noise) |
SV2 is the 3 pin connector next to the MAX232 chip, near the regulator and EC18. Pin 1 on SV2 is the "top" pin, with GND on the side closest to the EconoSeal loom connectors.
Only the SV2 header is populated. The pinout of SV1 is the same. Pin 3 of SV1 is the pin closest to Pin 1 of SV2.
The EC18-pin 14 and 15 are otherwise free pins that are often used (eg. fully assembled units shipped recently) for RS322.
DB9 works well but using a 1/4" earphone plug looks cleaner in an automotive enviroment. Even if 3.5mm plugs is used in the Autronic harness their manual recommends using 1/4" plugs if it's installed in a panel. This is a good advice, go with the 1/4" plug. The biggest problem with 3.5mm is that most of the female connectors are low quality and will cause problems with time.
DB9 (==DSUB9) connector for PC/Genboard Communication:
Please share the sources for above image. It counterrecmomends EC36-26 as GND for some unknown reason (EC36-pin26 is fine for this purpose).
How to use FBUS connection - TODO: detail
useful with a device (or adapter cable) that doesn't have -+8V compatible RS232, just 0/3V serial connection (like PDA-s, mobile phones and their accessory-cables).
Also good for bypassing the MAX232 for testing (eg. if MAX232 was killed by swapped RX-TX).
For the PC=>AVR direction the trick is to tap onto the AVR-side of R52(=2k7, between the mcp3208 chip and LCD connector) to prevent conflict with the output of MAX232 (without unsoldering the MAX232).
The AVR => PC direction is easy, there should be no conflict with the MAX232's input (several inputs can listen on the same bus while only one can drive at a time).
See UsbToFbus.
See also