CH341a Serial Mode

[mmartell]

I'm trying to program a Metra Axxess ASCW, it's a unit that enables you to retain steering wheel controls when installing an after market stereo in your car. The newer units use a micro usb to program this one has four pins, GND RX TX +5v.

My CH341a programmer runs natively at 3.3v. My question is if I bypass the 3.3v regulator will the chip accept the 5v supply and will the TTL signals become 0/5v ?

[mmartell]

My CH341a Programmer

[m1ch43lzm]

Hi, according to CH341A datasheet the chip supports 5v and 3.3v input, and for 5V operation, pin 9 should be connected to a capacitor (page 3 of datasheet) and should not be fed with external power

> will the chip accept the 5v supply and will the TTL signals become 0/5v ?
Yes to both questions

For 3.3v operation according to datasheet 3.3v should be connected also to pin 9 and 28 (page 7 from datasheet), yet on my programmer there's no connection from pin 9 to 28 and it works fine

My programmer looks similar to yours, except the PCB is green, and +5v next to +3.3v on the header pins

You could lift pin 28 and connect to +5V from USB, or cut the trace (marked in red), check first continuity from pin 28 to pin 9, should be open
Also check continuity from pin 9 to a nearby capacitor (on mine is marked with a yellow line on the attached picture)

[mmartell]

The 5v pin on your board seems to be on purpose - a jumper between there and the 3.3v pin supplies 5v to Vcc of the CH431a. It also puts 5v on the output of the LDO not sure if it will appreciate that or not lol.

I can remove the regulator with hot air and run a jumper. Thanks for the input.

[clearchris]

Most 5v chips can be programmed at 3v3. I'd try it out.

[mmartell]

Already tried and no go, unless I'm making some other mistake...

[stj]

so you want to use it as a serial adapter, then you need it to be in serial mode.
when programming chips it's in parallel mode.

probably the P/S jumper.

link TX and RX and run Putty.
see if you can type stuff and see it echo'd back.

[mmartell]

No I've changed the jumper but I did not verify it working with Putty. Will try that. Thanks.

[m1ch43lzm]

Found this schematic
https://www.onetransistor.eu/2017/08...schematic.html

It's from a different PCB, where the design (not sure if intentional or by mistake) outputs 5v levels, but the ZIF socket is powered with 3.3v , you can compare the schematics on that page

Make sure you also installed the correct drivers for serial mode (P/S jumper should be open for serial, closed for parallel), check also on Device Manager under Ports (COM & LPT), should be listed as "USB-SERIAL CH341A"
Drivers: http://www.wch.cn/download/CH341SER_ZIP.html

You can measure voltage on Tx pin to confirm

[mmartell]

I removed the 3.3v regulator and jumpered its 5v input to the output and still can't get it to work. It shows up in device manager but the software used to communicate with the device never finds it.

[mmartell]

I made a little progress on this. Turns out the CH341 is incompatible with this unit as the software is "looking" for an FTDI chip.

So I have one here it's a USB-Serial Port adapter. When I run the software it says "Four pin cable detected, looking for programmable unit..." which is good. But serial signals are incompatible with the unit.

What's the easiest way to go from Serial to TTL ?

[stj]

what software??
and to fix your FTDI cable, just open it and remove the level shifter - probably a max202 or similar

[mmartell]

https://www.axxessupdater.com/

Can't access the chip(s) they are inside the cable somewhere can't even see them.

[megaraider]

What a lame update app! For serial com it only imports 'FTD2XX.dll'
Make sure you install the correct FTDI drivers, it might only work with some limited versions (use drivers available under %PROGRAMFILES%\Axxess Updater\drivers);
Make sure you've got the COM port listed under 'Device Manager';
Many adapters are powered by the slave side (for extended compatibility with 3.3V and 1.8V) thus make sure the 5V pin is hot;

[mmartell]

Originally Posted by megaraider

What a lame update app! For serial com it only imports 'FTD2XX.dll'
Make sure you install the correct FTDI drivers, it might only work with some limited versions (use drivers available under %PROGRAMFILES%\Axxess Updater\drivers);
Make sure you've got the COM port listed under 'Device Manager';
Many adapters are powered by the slave side (for extended compatibility with 3.3V and 1.8V) thus make sure the 5V pin is hot;

It only supports FTDI because they sell an overpriced cable to do the updating using that chip.

Yes I have a com port listed under Device Manager.

I'll have to look up that file path to see what you mean exactly...

Which 5v pin are you referring to ? I don't think there is a 5v pin on the serial port end - I've been powering the unit externally with 5v.

[mmartell]

I looked up that file path but the info listed under /drivers is over my head. How do I tell if my drivers are compatible ?

[megaraider]

Originally Posted by mmartell

It only supports FTDI because they sell an overpriced cable to do the updating using that chip.

... 80 bucks

Originally Posted by mmartell

Which 5v pin are you referring to? I don't think there is a 5v pin on the serial port end - I've been powering the unit externally with 5v.

The 5V pin on the ASCW unit. (btw, power up it too -the ASCW)
If you're using a cable adapter this is even more relevant.

Originally Posted by mmartell

I looked up that file path but the info listed under /drivers is over my head. How do I tell if my drivers are compatible?

From what i've seen on those files you want to check if your listed "USB Serial Port" driver match:
DriverVer=10/06/2014, v5.1.2600.9 and/or DriverVer=03/09/2016, v2.12.16

[mmartell]

Great will have a look to see if my software matches those listed.

Yes I'm powering the aswc externally. The procedure is to have the USB-TTL cable plugged in and run the software THEN plug the unit into the cable. I wonder if I'm missing a timely reset by having the unit pre-powered and so not entering program mode ?

[megaraider]

Originally Posted by mmartell

I wonder if I'm missing a timely reset by having the unit pre-powered and so not entering program mode ?

The demo video mentions both: turn on the ignition key (power up the ASCW module) and don't.
Thus try out both!

[rivetcity]

Originally Posted by clearchris

Most 5v chips can be programmed at 3v3. I'd try it out.

Same thought here. It's really a question of bitbanging or transiting between high and low level. In almost 100% of cases a chip running at 5V will recognize 3.3V as High level. So don't modify anything. Make sure to have the same GND between the programmer and the device to be programmed. Supply 3v3 to your programmer, connect the RX and TX lines of the device you wanna flash to the TX and RX of your programmer and you should be good to go.

I would make sure to select the proper baudrate.