1. As Chris mentioned before the 87C552 TIMER2 can't be used as baudrate generator because it has different structure as "classic" 32 and has capture and compare facilities.

2. AFAIK the 87C552 has 3 versions: 12MHz, 16MHz and 24MHz version, so you must use 24MHz version if you can generate 115200Bd, because ...

3. ... in case you can generate 115200 Bd exactly there is only 22.1184MHz Xtal available (SMOD=1). But...

4. in case you need to receive 31250 Bd in rxd, there is not possible to set 31250 Bd with 22.1184MHz Xtal (38400.00 or 28800.00 only). You can compare it here: http://www.keil.com/c51/baudrate.asp.

I am afraid but this isn't task for the P87C552 hardware by my opinion.

Vaclav