Serial console to CRS328-24P-4S+

Hardware MikroTik hardware general
1

Hello forum,

I am looking to connect to the serial console port of my CRS328-24P-4S+ switch. I am looking to take an RJ45 Cat 5 cable wired to T-568B standard on one end and pins 3 and 6 connected to this USB to TTL board: https://www.amazon.com/dp/B0DLGQ9RXW

Has anyone done this successfully? When I connect using a baud rate of 115,200 to match my switch, I get garbage characters printed to the console or a string of C characters.

root@nexus:~# tio /dev/ttyCH343USB7
[11:30:05.448] tio v3.9
[11:30:05.448] Press ctrl-t q to quit
[11:30:05.448] Connected to /dev/ttyCH343USB7
C6

  CCCCCC
2

That USB thingy seems TTL.
The serial is RS-232.
Within limits, TTL can be considered a subset of RS-232 BUT it has inverted logic, so even if the 0-5V of the TTL is correctly sensed by the RS-232 0’s will be 1’s and viceversa. Additionally (it depends on the RS-232 on the Mikrotik side voltage and on the tolerance of the TTL converter) there is a risk of frying the TTL adapter:
https://www.nicerf.com/news/rs232-rs485-and-ttl.html

In any case it is not a very good idea to use only two wires a ground is usually needed.

You might need an adapter more like this one:
https://www.amazon.com/WWZMDiB-USB-RS485-RS232-Converter/dp/B0BL3NJTBJ/

1 Like
3

Use Cisco RJ45-DB9 cable + decent RS232 adapter.

4

This must be my issue, I thought the adapter I purchased was RS232 but in fact it’s TTL.

5

Or, there exist USB-terminated Cisco cables that combine both functions.