Dear VEMS v3.x mainboard owner,  (last updated 2015-04-14)

Some illustrated help available for VEMS genboard v3.x mainboard home assembly ( not for ECUs purchased assembled)
If you have purchased
https://shop.vems.hu/catalog/genboard-p-29.html

Please check http://vems.hu/files/genboardv3/assembly/v3.8/
(or notify whoever is doing the assembly).

Notably the
v3_mainboard_homeassembly_srl_9900-10499.pdf

Not many are using the third trigger, but probably the mcp3208/ch5 is useful.
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Atmega startup, RESET

With this solution SCK getting pulled up "strong and quick" to +5V while AVR RESET is being DELAYED, pulled up slow to +5V or +4.55V:
* Ru26=10k pullup (between +5V and atmega128/pin20 reset)
* SCK pullup=4k7 or min 2k2 pullup between +5V and (atmega128/pin11=SCK) SCK (bottom side, diagonally under the ISP / SDcard daughterboard header)
** note: if SD card is installed 2k2 or 2k35 recommended (eg. a 4k7 on the SD-card PCB, parallel with the mainboard 4k7, diagonally soldered the same way)
* Creset=220nF between GND and AVR reset
* optional: Ropt=100k pulldown between GND and reset (this can be piggybacked on top of the 220nF soldered above)
* optional: R53=0 Ohm instead of 1k (marked 1001, pic bottom left)


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Recently, 2015-03, some atmega instances were found to be sensitive to SCK/reset on powerup.
Eg starts 99% of the times... but in 1% not: the CEL (check engine light, which should always be connected) indicates this.

Now every assembled VEMS v3 must pass an automated 200..1000 startup(+comm) test before delivery.

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When ordering
https://shop.vems.hu/catalog/genboard-p-29.html
you can request "please include an mcp809 either soldered or a rescue kit item" if you like, no extra charge.
While the above SCK pullup and reset pullup solution provides fastest instant startup,
and mcp809 adds 400msec delay, mcp809 assures startup always, under
the weirdest conditions (eg. if ECU powered down for less than a half second only, and than powered up again).
 
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Generic notes, Just in case:

Do NOT use ISP on the mainboards, because uhex bootloader is already on, and ISP is locked (so ISP can do no good at all).

Connect all 5 grounds (EC36/pin 5, 21,22, 32, 26) also when supplying  ECU from a separate harness (eg. on bench).
Powering the board without EC36/pin26 and at least 2 other GND-s connected damages the TPIC6A259 "p259" chip and perhaps other components also.