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K25C81-FB Datasheet(PDF) 3 Page - Semtech Corporation |
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K25C81-FB Datasheet(HTML) 3 Page - Semtech Corporation |
3 / 12 page FUNCTIONAL DESCRIPTION PIN DEFINITIONS Copyright Semtech, 1997-2001 DOC5-C81-DS-105 www.semtech.com 3 Mnemonic DIP PLCC QFP TYPE Name and Function Vcc 40 44 38 I Power Supply: +5V Vss 20 22 17 I Ground OSCI 39 43 37 I Oscilator Input OSCO 38 42 36 O Oscilator Output _RESET 1 1 41 I Reset: apply 0 V to provide orderly start-up. _IRQ 2 2 42 I Must be tied to Vcc VX 3 4 43 I Tie to Vcc. RP 672I Rollover Mode Selection: tie to Vcc to select N-Key Rollover. Tie to Ground to select Two-Key Inhibit Mode. KC 894I/O Keyboard Clock: connects to PC’s keyboard port Clock Line. KD 783I/O Keyboard Data: connects to PC’s keyboard port Data Line. EKD 10 11 6 I/O External Keyboard Data: connects to external keyboard Data Line. EKC 9 10 5 I/O External Keyboard Clock: connects to external keyboard Clock Line. EKC1 37 41 35 I External Keyboard Clock 2: connects to external keyboard Clock Line and is used to generate an interrupt for every Clock Line transition. This signal must be inverted for PC/XT keyboards. C0-C7 12-19 3-17 8-15 O Column Select Outputs: select 18 one of columns. 19-21 C8-C15 28-21 31-24 26-18 C16 11 12 7 O C17 4 5 44 I/O Keyboard type selection: this pin is used both as outputs for column select and as input for standard keyboard-type selection. R0-R5 29-34 32-37 27-32 I Row data inputs R6 561I R7 36 39 34 I NC 35 38, 3 16, 33 - No Connects: these pins are 18, 23 22, 39 - unused. 40 40 Note: An underscore before a pin mnemonic denotes an active low signal. The FlexiCoderTM consists of six major sections (see functional diagram, previous page). These are the Keyboard Encoder, the Mode Control Unit, the PC Communication Channel, the 8042 Emulation Channel, the Interrupt Control Unit and the Data Buffer. These sections communicate with each other and operate concurrently. The controller continuously scans a keyboard organized as an 8 row by 18 column matrix, for a maximum of 144 keys. Smaller-size keyboards can be connected provided that all unused row pins are connected to Vcc. The microcontroller selects one of the 18 column lines (C0-C17) every 512 µS and then reads the row data lines (R0-R7). A key closure is detected as a zero in the corresponding position of the matrix. A complete scan cycle for the entire keyboard takes approxi- mately 9.2 mS. Each key press is debounced for a period of 20 mS. Once the key is verified, the corresponding key code(s) are loaded into the transmit buffer of the PC Keyboard Communication Channel. |
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