Intel mcs-48 manual 827918279·5

827918279·5

FUNCTIONAL DESCRIPTION

Since data input and display are an integral part of many microprocessor designs, the system designer needs an interface that can control these functions without placing a large load on the CPU. The 8279 provides this function for 8-bit microprocessors.

The 8279 has two sections: keyboard and display. The keyboard section can int'erfaceto regular typewriter style keyboards or random toggle or thumb switches. The display section drives alphanumeric displays or a bank of indicator lights. Thus the CPU is relieved from scanning the keyboard or refreshing the display.

The 8279 is designed to directly connect to the microprocessor bus. The CPU can program all operating modes for the 8279. These modes include:

Input Modes

•Scanned Keyboard - with encoded (8 x a key keyboard) or decoded (4 x a key keyboard) scan lines. A key depression generates a 6-bit encoding of key position. Position and shift and control status are stored in the FI FO. Keys are automatically debounced with 2-key lockout or N-key rollover.

•Scanned Sensor Matrix - with encoded (8 x a matrix switches) or decoded (4 x 8 matrix switches) scan lines. Key status (open orclosed) stored in RAM addressable by CPU.

•Strobed Input - Data on return lines during control line strobe is transferred to'FIFO.

Output Modes

•a or 16 character multiplexed displays that can be or- ganized as dual 4·bitor single a-bit (80 =Do, A3 =07)'

•Right entry or left entry display formats.

Other features of the 8279 include:

• Mode programming from the CPU.

eClock Prascaler

•Interrupt output to signal CPU when there is keyboard or sensor data available.

•An 8 byte FIFO to store keyboard information.

•16 byte internal Display RAM for display refresh. This RAM can also be read by the CPU.

elK RESET DBO-l IRa

KEVBOARD

DEBOUNCE

AND

CONTROL

TIMING

AND

CONTROL

OUT Ao., OUT Bg.3 iii SLO·3 RLO.7 CNTLISTB

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