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By newbie123
#202281
Hello Everyone.
I want to use a SparkFun Serial Basic Breakout - CH340G to power an avr programmer (avr911 programmer) and communicate with the PC side at 115200 baud rate.
Both the avr and the target will be using 3.3V.

The avr programmer will take power from pin 4 of the CH340G (3.3V).

I have searched everywhere for a clear answer. The datasheet for the CH340 is in Chinese.
I have found some translations but they are not clear regarding the 3V output of the CH340G.
The datasheet on Sparkfun is not for a CH340"G". (it's for a CH340T, CH340R, CH340H, these are all 20 pin Ch340's).

Regarding the 3V3 pin, the datasheet says:
Code: Select all
connects of VCC to input outside power while 3.3V, connects of 0.01uF decoupling capacitance outside while 5V
I think that means that the 3.3V pin connects to the input of other devices (in my case the programmer and the programmers' target)

When using 5V, connect this pin to 0.01uF capacitor.

Basically the programmer and targets' VCC will be connected to this pin.
The CH340G will get power from the USB port (5V).

What I am wondering is:
What will the logic levels out of the CH340G be?

If the programmer expects 3V logic levels on the RXD pin and the CH340G outputs 5V logic levels wouldn't that destroy the input? I don't want to damage anything.

I am not worried about the target because both the programmer and the target will be running @ 3.3V.

I want to borrow a scope to check it out but I thought I would ask here first.

I thought of installing a 1K series resistor to the programmers RXD pin just in case.
Any thoughts?
User avatar
By chipace
#203633
Without any modifications to ch340g, all signals levels will be 3.3V. There is a board option for 5.0V where you can cut a trace and solder 2 pads. I wish that they would have implemented a jumper... but it is probably safer for beginners to be limited to 3.3v.
No resistors needed. The ch340g's VCC and GND pins should be able to power your AVR, and the DTR, CTS, TX and RX pins will be at 3.3V by default (control signals are active low).

I use Ubuntu 18.04 and it automatically detects the ch340g as ttyUSB0. I have used 115200 and 921600 baud rates.