The 8255A is a general-purpose programmable l/O device designed for use with Intel microprocessors. It has 24 O pins which may be individually programmed in 2 groups of 12 and used in 3 major modes of operation. In the first mode (MODE 0), each group of 12 /0 pins may be programmed in sets of 4 to be input or output. In MODE1, the second mode, each group may be programmed to have 8 lines of input or output.
8255 Pin Configuration
| Pin Number | Pin Name | Description |
|---|---|---|
| 1-4 | PA0-PA3 | Port A |
| 5 | RD | Read (Active Low) |
| 6 | CS | Chip Select (Active Low) |
| 7 | GND | Ground |
| 8 | A0 | Address Input |
| 9 | A1 | Address Input |
| 10-17 | PC0-PC7 | Port C |
| 18-25 | PB0-PB7 | Port B |
| 26 | Vcc | +5V Power Supply |
| 27-34 | D0-D7 | Data Bus |
| 35 | RESET | Reset Input |
| 36 | WR | Write (Active Low) |
| 37-40 | PA4-PA7 | Port A |
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