- These are two basic modes of operation of 8255. I/O mode and Bit Set-Reset mode (BSR).
- In I/O mode, the 8255 ports work as programmable I/O ports, while in BSR mode only port C (PC0-PC7) can be used to set or reset its individual port bits.
- Under the I/O mode of operation, further there are three modes of operation of 8255, so as to support different types of applications, mode 0, mode 1 and mode 2.
8255A: BSR(Bit Set/Reset) Mode
- In this mode any of the 8-bits of port C can be set or reset depending on D0 of the control word.
- The bit to be set or reset is selected by bit select flags D3, D2 and D1 of the CWR (Control Word Register).
- BSR Control Word affects one bit at a time
- It does not affect the I/O mode
