Connecting the serial port is very easy, it's only 3 wires, GROUND is one of them
GROUND is really important, often neglected, and in some cases, confusingly "connection kinda works apparently", but unreliable (eg VemsTune connects, but error during firmware upload).
- either missing ground connection.
- eg. EC18/17 can be 2nd heater FET (NFET) output, or input; so use EC36/26 as signal ground, do NOT assume that EC18/pin17 is GND (especially when swapping ECUs; maybe it was GND in old ECU, and not on the new; DVM diode mode measurement is quick and useful: 0mV indicates wired connection).
- in trickier cases, ground loops can also cause noise (communication problems). Eg. some notebook chargers can cause interference.
On the ECU, DSUB9 female is used for RS232 (since the PC is DSUB9/male).
ECU DSUB9 male is LCD so do NOT try to connect RS232 to that with any kind of adapter => damage could result.
RS232 is widely used, see [rs232 pinout]. Note that DSUB25 (which is almost never used) standard has TX-RX swapped compared to [DSUB9]. (DSUB=DB).
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 (DSUB9/pin5) inside the (min. 3 wires + shield) cable. The cable should preferrably not run alongside ignition (or other noisy) wires.
| DB9 female | Direction | SV2 | EC18 | Earphone plug | |
| 3 | --> | 1 | EC18-pin14 | RING | Data transmitted by PC DB9M/3, received by VEMS ECU |
| 2 | <-- | 2 | EC18-pin15 | TOP | Data received by PC DB9M/2, transmitted by VEMS ECU |
| 5 | <-> | 3 | EC36/26 GND | Base | EC36/26 Ground. Avoid EC18/17 which can be 2nd WBO2 heater depending on ECU options! |
. Check your adapter specs ||
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 by default) for RS322.
DB9 works well but using a 1/4" earphone plug is also possible in cabin (not in engine bay, since more sensitive to splashing water). 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 (also shorted out during plugin and disconnect).
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