DMX512A is a serial protocol developed for the control of stage lighting that allows up to 512 channels of control on a single pair of wires. The use of a pair of wires allows for the use of RS485 which is a balanced signal that provides for noise immunity. The RS485 signal needs to converted to an unbalanced signal that can be fed into the microcontroller used in the lighting fixture.
Altronics sell a TTL to RS485 Breakout Module Z6364 to convert the RS485 to a TTL signal suitable for the Arduino Serial Input, or convert the TTL signal from the Serial Output to an RS485 signal.
Protosupplies have documented this module https://protosupplies.com/product/max485-ttl-to-rs-485-interface-module/ and you can copy the Arduino code to try it.
This module uses the Arduino D0 RX and D1 TX ports for DMX serial communications, so you need to disconnect the module from the RX and TX ports when you want to program the Arduino unit. You will not be able to easily use the Serial monitor when using this module.
Altronics sell a DFROBOT Z6548 DRF0259 RS485 Shield For Arduino https://www.altronics.com.au/p/z6548-dfrobot-dfr0259-rs485-shield-for-arduino/ .
The wiki for DFROBOT Arduino RS485 Shield is https://wiki.dfrobot.com/Arduino_RS485_Shield_SKU__DFR0259 and has test code.
Barbizon have a series of Things You Should Know posters at https://www.barbizon.com/literature/ which includes about DMX, Art-Net, Streaming ACN and RDM .
This chart is useful for wiring DMX adaptor leads.
This page updated 27 January 2021