The 8255 is a popular programmable peripheral interface (PPI) chip that is often used to expand the input/output capabilities of a microcontroller. It provides three 8-bit ports, referred to as Port A, Port B, and Port C. Each port can be configured as either input or output.

In order to interface the microcontroller with the 8255, certain pins need to be connected between the two devices. The pins that are directly connected between the microcontroller and the 8255 are as follows:

1. RD (Read): This pin is used by the microcontroller to read data from the 8255. It is connected to a control pin on the microcontroller that is responsible for initiating a read operation.

2. WR (Write): This pin is used by the microcontroller to write data to the 8255. It is connected to a control pin on the microcontroller that is responsible for initiating a write operation.

3. D0-D7 (Data): These pins are used to transfer data between the microcontroller and the 8255. Each pin corresponds to one bit of data, allowing for the transfer of 8 bits at a time.

These pins are directly connected between the microcontroller and the 8255 to enable communication and data transfer between the two devices. The RD and WR pins are used to control the flow of data, while the D0-D7 pins are used to transfer the actual data.

By connecting these pins correctly, the microcontroller can send data to the 8255 for output or read data from the 8255 for input. This allows for increased flexibility and expanded input/output capabilities in the microcontroller system.

In conclusion, all of the mentioned pins (RD, WR, D0-D7) of a microcontroller are directly connected with the 8255 chip in order to facilitate data transfer and communication between the two devices.