You should always look to the manufacturer's own website first for information on their products - in this case, it's
http://www.vishay.com (not .de as it says in that datasheet!)

However, Vishay don't list this part - it's not even in their obsolete list - so it's presumably very old?
Hence the incorrect website address?

So, now we can see that this device is an SIR Transceiver.
This is the IR equivalent of the MAX232 et al transceivers for RS232 - it's what converts between logic-level signals and infrared light.
It includes the IR emitter and the IR detector.

Vishay's current site for IR transceivers is http://www.vishay.com/ir-transceivers/

On the right-hand side of that page are two documents:
IRDA Basics
Part 1: IrDA® Physical Layer: http://www.vishay.com/doc?82513
Part 2: Software Protocol: http://www.vishay.com/doc?82504

The "IrDA® Physical Layer" document shows you how to use an IR transceiver with a UART - see fig 1 on p3
(it shows a 16550 UART - you're using the internal UART of an 8051)

As I said to you originally, you should always check-out the manufacturer's website for supporting information like this.
This document is key to understanding what's going on!


This one is on the Vishay site:
http://www.vishay.com/ir-transc...lete-list/
http://www.vishay.com/doc?82546
Again, it's obsolete.

This is an Encoder/Decoder: it's what converts the UART signals into the pulse format required for IR see p6 of the "IrDA® Physical Layer" document



This is a complete IRDA Protocol Stack in hardware.
Again, it goes between the UART and the IR transceiver, as shown on p4.
I'm sure Microchip will have plenty of supporting documentation for this on their website...