Consider...

HSERIN [bilgi]

... at 9600 baud means you're sending 9600 bits in a second... for arguments sake, say it takes 10 bits for one byte (with start and stop bits), so it takes less than 1mS per byte to receive...

And now...

write b, bilgi

...takes 10mS to write to EEPROM...

So for every ONE byte you save to EEPROM, using your code/method at only 9600 baud will ensure you lose the following 10/12 bytes of incoming data. Can you now see it's not so straightforward to receive RS-232 and write it to EEPROM... as you have to make sure that when you write to your EEPROM you're still going to grab any incoming data that may be arriving at the same time.