KEYBOARD/DISPLAY INTERFACE. UPD8279-5 Datasheet
NEe Microcomputers, Inc.
The ~PD8279-5 is a programmable keyboard and display Input/Output device. It
provides the user with the ability to display data on alphanumeric segment displays
or simple indicators. The display RAM can be programmed as 16 x 8 or a dual
16 x 4 and loaded or read by the host processor. The display can be loaded with
right or left entry with an auto-increment of the display RAM address.
The keyboard interface provides a scanned signal to a 64 contact key matrix expand-
able to 128. General sensors or strobed keys may also be used_ Keystrokes are stored
in an 8 character FIFO and can be either 2 key lockout or N key rollover. Keyboard
entries generate an interrupt to the processor.
• Programmable by Processor
• 32 HEX or 16 Alphanumeric Displays
• 64 Expandable to 128 Keyboard
• Simultaneous Keyboard and Display
• 8 Character Keyboard - FIFO
• 2 Key Lockout or N Key Rollover
• Contact Debounce
• Programmable Scan Timer
• Interrupt on Key Entry
• Single +5 'i/olt Supply, ±10%
• Fully Compatible with 8080A, 8085A, ~PD780 (ZOOTM)
• Available in 40 Pin Plastic Package
Data Bus (Si-directional)
Interrupt Request Output
Display (AI Outputs
Display (BI Outputs
Bland Display Output
TM: Z80 is a registered trademark of Zilog.
The /.lPD8279-5 has two basic functions: 1) to control displays to output and 2) to
control a keyboard for input. Its specific purpose is to unburden the host processor
from monitoring keys and refreshing displays. The /.lPD8279-5 is designed to directly
interface the microprocessor bus. The microprocessor must program the operating
mode to the /.lPD8279-5, these modes are as follows:
• 8 or 16 Character Display
• Right or Left Entry
• Scanned Keyboard with Encoded 8 x 8 x 4 Key Format or Decoded 4 x 8 x 8
• Scanned Sensor Matrix with Encoded 8 x 8 or Decoded 4 x 8 Scan Lines.
• Strobed Input.
elK RESET 080_7
OUT AO_3 OUT 80-3
...... OOC to +70°C
Storage Temperature ......... .
. _65°C to +125°C
All Output Vol tages .. .
. . . . . . . . . . . . . . . . . . .. -0.5 to +7 Volts<D
All Input Voltages. : . . . . . . . . . .
-0.5 to +7 Voits<D
Supply Voltages .... .
-0.5 to +7 Volts<D
Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1W
CDNote: With respect to VSS
CO'MMENT: Stress above those listed under "Absolute Maximum Ratings" may cause permanent
damage to the device. This is a stress rating only and functional operation of the device at these or
any other conditions above those indicated in the operational sections of this spe~ifjcation is not
implied. Exposure to absolute maximum rating conditions for extended periods may affect device
-1-0- - .. -- RD
Return Li nes
Return line inputs which are connected to the scan
lines through the keys or sensor switches. They
have active internal pullups to keep them high until
a switch closure pulls one low. They also serve as an
8·bit input in the Strobed Input mode.
Clock from system used to generate internal timing.
Interrupt Request. In a keyboard mode, the inter·
rupt line is high when there is data in the FIFOI
Sensor RAM. The interrupt line goes low with each
FIFOISensor RAM read and returns high if there
is still information in the RAM. In a sensor mode,
the interrupt line goes high whenever a change in a
sensor is detected.
A high signal on this pin resets the IlPDB279·5.
Input/O:-,tput read and write. These signals enable
the data buffers to either send data to the extemal
bus or receive it from the external bus.
Bi-Directional data bus. All data and commands
between the processor and the IlPDB279·5 are
transmitted on these lines.
Power Supply Ground
Buffer Address. A high on this line indicates the
signals in or out are interpreted as a command or
status. A low indicates that they are data.
Chip Select. Alow on this pin enables the inter·
face functions to receive or transmit.
Blank Display. This output is used to blank the
display during digit switching or by a display
These two ports are the outputs for the 16 x 4
display refresh registers. The data from these out·
puts is synchronized to the scan lines (SlO·Sl3)
for multiplexed digit displays. The two 4-bit ports
may be blanked independently. These two ports
may also be considered as one B·bit port.
Scan Lines which are used to scan the key switch
or sensor matrix and the display digits. These
lines can be either encoded (1 of 16) or decoded
,The shift input status is stored along with the key
position on key closure in the Scanned Keyboard
modes. It has an active internal pullup to keep it
high until a switch closure pulls it low.
For keybo'ard modes this line is used as a control
input and stored like status on a key closure. The
line is also the strobe line that enters the data into
the FIFO in Strobed input mode !Rising Edge), It
has an active internal pullup to keep it high until
a switch closure pulls it low,
Power Supply Input