I have a premium FTDI converter cable as well as a cheaper Prolific one. They seem to work equally well with Atmel chips, whereas some SoCs (e.g. MStar) create issues.framp wrote: ↑Do you have any converter you can recommend?
They can be obtained from sites like Adafruit.com, or if you can spare the delivery delay, Aliexpress.com.
Just be sure that the "cable" is for 3.3V signal levels rather than 5V TTL.
With a USB serial converter, you should not need to make any Vcc connection or use the red wire of the USB "cable".framp wrote: ↑I found some which have GND, RxD, TxD, DTR/RTR and CTS and Vcc (3.3 V or 5 V) . As far as I understand I have to use a Vcc 3.3 V converter. You mentioned Pin 1 or Pin 4 to be Vcc. This makes me nervous because I don't want to create a short circuit and destroy the UART interface electronic and I have to be carefully with GND and Vcc.
You would need to use the Vcc when connecting a RS-232 transceiver, because it needs power.
With a USB serial converter (which is powered by its PC host) you do not have to make any additional power connections.
You can start testing with just a ground connection (i.e. the black wire) and the TxD wire (e.g. the yellow wire of the FTDI or the white wire of the Prolific "cable"), and probe for console output (right after a board reset) on pin 1 or 4.
Only after you manage to find/identify the UART's TxD should you probe for the RxD.
If you want to play it safe, then only make connections when the board is not powered. That is actually prudent, since these TTL pins are not intended for hot-plugging and have no ESD protection.
Getting a new serial connection to work can sometimes be a real pain (confusing labels, crossed wires, matching port settings, etc.). I often have to resort to tracing the signals to break down the problem.framp wrote: ↑I understand a scope will help to better identify the pins. Do you have any recommendation for a cheap scope I can buy?
But there are too many variables to consider for any quick recommendation.
A PC-based 'scope can be less expensive than a standalone unit, but the software is typically Windows-only and setup takes longer.
There are some dinky, toy-like 'scopes for less than US$20 that should be able to capture a 115200 baud frame, but would you really rather have two (or more) channels, more bandwidth, more capture memory?