Most notably, this will allow experimentation with the W65C22 VIA (Versatile Interface Adapter), and the W65C51 ACIA (Asynchronous Communications Interface Adapter).
This is despite the known Transmit Data Register Empty (TDRE status register flag) bug with the W65C51N ACIA.
For reference, here is the note (regarding the bug), as it is documented in WDC's W65C51 datasheet:
Significantly, both the VIA and ACIA devices remain in current production by the Western Design Centre Inc (WDC).Note:
The W65C51N has an operation issue concerning TDRE. This bit is not being reset after loading the
Transmitter Data Register. Polling the TDRE bit of the status register will never show the TDR as Empty.
Due to this issue, the W65C51N is not suggested as a direct replacement for older 6551 devices if the
firmware uses this bit. It is recommended to using IRQ handling or software timeout for transmission as a
workaround for this issue.