The board I used to test T89C... is a board where AT89S53 had been mounted. It's a device which communicates normally on RS485 bus, but when a PC COM is attached it turns to RS232, and communicates with the user. Just forget about inverting HC00, it's not the only one after MAX232 and that's something that surely is OK.

But the question is - how a standard CMOS output cannot drive the RXD input ? And with ...S53 is perfect.

The second chip I had, I mounted on another board, and got nearly the same picture on the scope.

I tried with and without EA tied to GND - the same !

Regards, Slobodan