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STV3012 bảng dữ liệu(PDF) 6 Page - STMicroelectronics |
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STV3012 bảng dữ liệu(HTML) 6 Page - STMicroelectronics |
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6 / 8 page  I.4 - Oscillator Input and Output The external components must be connected to these pins when using an oscillator with a ceramic resonator. The oscillator frequency may vary be- tween 350kHz and 600kHz as defined by the reso- nator. No external feedback resistor is allowed. II - FUNCTIONAL DESCRIPTION Key operation (see Figure 3) : In the stand-by mode all drivers (DRV0N to DRV6N) are on (low impedance to VSS). Whenever a key is pressed, one or more of the sense inputs (SENnN) are tied to ground. This will start the power-up sequence. First the oscillator is activated and after the debounce time tDB the output drivers (DRV0N to DRV6N) become active successively. Within the first scan cycle, the transmission mode, the applied sub-system address and the selected command code are sensed and loaded into an internal data latch. In contrast to the command code, the sub-system is sensed only within the first scan cycle. If the applied sub-system address is changed while the Command key is pressed, the transmitted sub-sys- tem address is not altered. In a multiple key stroke sequence the command code is always altered in accordance with the sensed key. III - OUTPUT SEQUENCE (DATA FORMAT) The output operation will start when the selected code is found. A burst of pulses, including the latched address and command codes, is generated at the output REMO as long as a key is pressed. The operation is terminated by releasing the key or if more than one key is pressed at the same time. Once a sequence is started, the transmitted data words will always be completed after the key is released. The toggle bits T1 and T0, during mode A only T0, toggle if the key is released for a minimum time tREL. The toggle bits remain unchanged within a multiple key-stroke sequence. IV - MULTIPLE KEY-STROKE PROTECTION The keyboard is protected against multiple key- strokes (Figure 4). If more than one key is pressed at the same time, the circuit will not generate a new output at REMO. In case of a multiple key-stroke, the scan repetition rate is increased to detect the release of a key as soon as possible. There are two restrictions caused by the special structure of the keyboard matrix : the keys switch- ing to ground (code numbers 7, 15, 23, 31, 39, 47, 55 and 63) and the keys connected to SEN5N and SEN6N are not covered completely by the multiple key protection. If one sense input is switched to ground, further keys on the same sense line are ignored, i.e. the command code corresponding to "key to ground" is transmitted. SEN5N and SEN6N are not protected against multiple keystroke on the same driver line, because this condition has been used for the definition of additional codes (code number 56 to 63). Figure 3 : Single Key-stroke Sequence. Debounce time : tDB = 4 to 9 x t0, Start time : tST = 5 to 10 x t0, Minimum release time : tREL = t0. OSCILLATOR ACTIVE scan scan new key new word scan key bouncing closed released off on REV DRVnN H L H L REMO OSCO t DB ST t W t REL t STV3012 6/8 |
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Mô tả tương tự - STV3012 |
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