When AMD launched the B550 motherboard chipset the company made it very clear that there will be no support for older and previous-gen AMD Ryzen CPUs.
The AMD B550 chipset wasn’t supposed to run 1st and 2nd generation of processors, including the Ryzen 5 3400G and Ryzen 3 3200G APUs for example, which are also basically based on the old “Zen+” micro-architecture.
To make this very clear, the B550 chipset only supports 3rd gen Ryzen Matisse CPU lineup, and is also ready for the upcoming Zen 3 based “Vermeer” desktop processors. The Ryzen 3000 Picasso APU lineup is not supported. Older gen Ryzen 2000 Pinnacle Ridge, Raven Ridge, and first gen Ryzen 1000 Summit Ridge processors aren’t supported either. The Athlon 200 and 3000 ZEN based chips also suffer the same fate. According to AMD, the company says that it ran into some “ROM size” limitations when trying to cram AGESA microcode for all the older processors.
As per AMD, the flash memory chips that store the BIOS have capacity limitations, and not all AM4-based motherboards feature dual-BIOS chip design (mostly found on the more expensive and high-end boards).
But now according to a recent leak which comes via the hardware enthusiast @momomo_us, one ASUS TUF Gaming B550M-Plus motherboard has been spotted running the “Zen+” Ryzen 5 3400G APU (Picasso silicon), and also the older Ryzen 5 2600X processor, which is based on the Pinnacle Ridge silicon. He posted CPU-Z validation screenshots for both these processors running on the B550 chipset. The second tweet from @momomo_us can be found here.
You can find the CPU-Z validation page for the 3400G/B550 entry over here, and the entry for the 2600X+B550 combo can be found here. As we can see the board is shown running the BIOS version 0608, which is dated 15/06/2020. Moreover, the ASUS motherboard’s official CPU support list page does not mention compatibility for the above two tested ZEN+ processors. But someone managed to run these processors on the B550 chipset, maybe via some hack or trick.
Nonetheless, I WON’T recommend buying/using the B550 chipset motherboard if suppose you are rocking an older gen AMD Ryzen CPU. There is no official word or support from AMD, as evident from this chart below. It is too risky to even try doing this.