Table des matières
8255 - Programmable Peripheral Interface - PPI (PC,XT, PCjr)
The Intel 8255 (or i8255) Programmable Peripheral Interface (PPI) chip was developed and manufactured by Intel in the first half of the 1970s for the Intel 8080 microprocessor.
The 8255 provides 24 parallel input/output lines with a variety of programmable operating modes.
The 8255 is a member of the MCS-85 family of chips, designed by Intel for use with their 8085 and 8086 microprocessors and their descendants.
It was first available in a 40-pin DIP and later a 44-pin PLCC packages.
It found wide applicability in digital processing systems and was later cloned by other manufacturers.
The 82C55 is a CMOS version for higher speed and lower current consumption.
The functionality of the 8255 is now mostly embedded in larger VLSI processing chips as a sub-function.
A CMOS version of the 8255 is still being made by Renesas but mostly used to expand the I/O of microcontrollers, the 82C55 for higher speed and lower current consumption.
This chip is present only on PC, PC-XT and PCJunior, for AT and later model (AT, PS/2), it was replaced by the 8042 Keyboard Controller
Pin-out
| PA0 - PA7 | Pins of port A |
|---|---|
| PB0 - PB7 | Pins of port B |
| PC0 - PC7 | Pins of port C |
| D0 - D7 | Data pins for the transfer of data |
| RESET | Reset input |
| RD | Read input (inverted) |
| WR | Write input (inverted) |
| CS | Chip select (inverted) |
| A0 - A1 | Address pins |
It consists of 40 pins and operates in +5V regulated power supply.
Port C is further divided into two 4-bit ports i.e. port C lower and port C upper and port C can work in either BSR (bit set rest) mode or in mode 0 of input-output mode of 8255.
Port B can work in either mode 0 or in mode 1 of input-output mode.
Port A can work either in mode 0, mode 1 or mode 2 of input-output mode.
It has two control groups, control group A and control group B. Control group A consist of port A and port C upper.
Control group B consists of port C lower and port B. Depending upon the value if CS’, A1 and A0 we can select different ports in different modes as input-output function or BSR.
This is done by writing a suitable word in control register (control word D0-D7).
PC / XT / Junior Mapping
| A0 | A1 | Selection | Address |
|---|---|---|---|
| 0 | 0 | PORT A (keyboard input/output buffer (output PCjr)) | 060h |
| 0 | 1 | PORT B Output | 061h |
| 1 | 0 | PORT C Input | 062h |
| 1 | 1 | Control Register | 063h |