Are there any instructions on how to use it? Send or receive Messages?

This is a "well behaved" product which seems to meet its specifications. I recommend this product for what it does. It works well for both send and receive. I have several of them. Serial communications can be a bit "tricky" so if you are not familiar with it, I recommend either a book or research on the internet. A full discussion of this subject is a bit beyond this forum. Good luck.

Would it work with rs422?

Currently, only RS485 is supported.

this item include the cables on the picture?

I don't know what picture you are looking at but - probably. The package included a 4 conductor cable approximately 12 inches long. It is designed to plug into the "TTL" end.

Does the tx go into high-z (tri-state) when not transmitting, so it can be used on modbus or multi-drop lines?

Yes. It works well with Modbus multi-drop lines as long as your "master" is working according to spec. For the price, just try it to be sure it works for you.

Brand	DSD TECH
Product Dimensions	5.08 x 1.78 x 1.78 cm; 15 g
Item model number	SH-U12
Manufacturer	DSD TECH
Color	blue
Processor Brand	Raspberry Pi
Processor Count	1
Wireless Type	802.11b
Hardware Platform	Arduino
Operating System	Raspberry Pi OS
Are Batteries Included	No
Item Weight	15 g

SH-U12 RS485 to TTL 5V Board with MAX13487 Chip for Raspberry Pi Arduino and Other MCU

Description

Specifications

Common Questions