Coupon Accepted Successfully!


Pin Diagram of 8279

DB0–DB7 (Bi-Directional Data Bus) These are bidirectional data bus. All data and commands between the CPU and the programmable keyboard interface 8279 are transferred on these lines.
CLK (Clock) Generally, a system clock is used to generate internal timing.
RESET A high signal on this pin is used to reset the 8279. After being reset, the 8279 is placed in the following mode:
  • 16 8-bit character display—left entry
  • Encoded scan keyboard—2 key lockout
  • The clock prescaler is set to 31
CS (Chip Select) A low on this pin enables the programmable keyboard interface, 8279 to receive or transmit data.
A0 (Buffer Address) A high on this line indicates that the signals in or out are interpreted as a command or status. A low on this line indicates that they are data.
RD (Read) This output signal is activated from microprocessor to 8279 to receive data from external bus.
WR (Write) This signal enables the data buffers to send data to the external bus.
IRQ (Interrupt Request) In keyboard mode, the interrupt line is high when there is data in the FIFO/Sensor RAM. The interrupt line becomes low with each FIFO/Sensor RAM read and returns high if there is some still information in the RAM. In sensor mode, the interrupt line goes high whenever a change in a sensor is detected.
SL0–SL3 (Scan Lines) Scan lines which are used to scan the key switch or sensor matrix and to select the display digits. These lines can be either encoded or decoded mode.
RL0–RL7 (Return Line) These are return line inputs. These are connected to the scan lines through the keys or sensor switches. They have active internal pull-ups to keep them high until switch closures are pulled down. The switches are connected between the scan lines and return lines. These lines also serve as an 8-bit input in the Strobed Input mode.
Shift (Shift) The shift input status is stored along with the key position on key closure in the scanned keyboard modes. Till a switch closure pulled low, it has an active internal pull up to keep it high.
CNTL/STB (Control/Strobed Input Mode) In keyboard modes, CNTL/STB line is used as a control input and stored like status on a key closure. The line can be used as the strobe line that enters the data into the FIFO in the strobed input mode. It has an active internal pull-up to keep it high until the line is pulled down with a switch closure.
OUT A0–OUT A3 and OUT B0–OUT B3 (OUTPUTS) These are the output ports for the 16 × 4 display refresh registers. The data from these outputs is synchronised to the scan lines (SL0–SL3) for multiplexed digit displays. The two 4 bit ports may also be used as one 8-bit port. These two ports may be blanked independently.
Pin diagram of 8279


The schematic diagram of 8279

BD (Blank Display) This output pin is used to blank the display during digit switching or by a blanking command.

Test Your Skills Now!
Take a Quiz now
Reviewer Name