PIN CONFIGURATION OF 8279

DB₀-DB₇-Typeinput/output. These are bidirectional input/output lines.

CS(CHIP SELECT)

Type-input 

This is an active low input signal used to select the 8279 for normal read or write operation.

RD(READ)

type-input

This is an active low signal and a low on this i/p enables the 8279 to send data to the MP. 

WR-

When this pin is low MP will write data or control words into the 8279. 

A₀-When it is high it indicates the transfer of a command or status info. and when this is low it indicates the transfer of data.

CLK-

Used to generate internal timings required by 8279. 

RESET-

During reset the clock presale is set to 31. 

IRQ-

When there is a data in FIFO sensor RAM the interrupt o/p goes high.

SL₀-SL₃- 

Used to scan the keyboard matrix and display digits.

RL₀-RL₇-

These lines are connected to one terminal of keys while the other terminal is connected to the decoded scan lines.

SHIFT-

In the scanned keyboard mode the status of the shift i/p line is stored along with each keys code in FIFO. 

CNTL/STB

Used as control i/p in the keyboard mode and stored in FIFO on a key closer.

BD

The o/ p pin is used to blank the display during the digit switching or by blanking display command. 

OUTA₀-OUTA₃ and OUTB₀-OUTB₃- 

These pins will work as the o/p ports .To scan the display & keyboard the data from these lines is synchronised with the scan lines. 

VCC-

This pin is used to provide power supply. 

GND-

This pin is used to provide ground.