hi,

maybe it does not help but I have yet another question:
you say that you replace AT89S53 with T89C51RD2. May I ask: why? I cannot understand next: AT89S53 is programmed with ISP-via-SPI and uses MISO/MOSI/SCK pins. T89C51RD2 is programmed via IAP+UART and uses RXD/TXD pins. Do you not mix this point?

By the way, some T89C51RD2 in PLCC/VQFP packages require extra GND connection (pin 1 of PLCC44 and pin 39 of VQFP44). I do not know why, but datasheet says about this pin: "Optional Ground: Contact the Sales Office for ground connection." As I use AT89C51RD2 so I have no idea what they mean by it.

Regards,
Oleg