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BS801B Datasheet(PDF) 7 Page - Holtek Semiconductor Inc |
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BS801B Datasheet(HTML) 7 Page - Holtek Semiconductor Inc |
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7 / 21 page  BS801B/02B/04B/06B/08B Rev. 1.00 7 July 7, 2009 lows three functions to be implemented, two are initiated by the external MCU and one by the BS80xB. SCD Command Direction Wake-up or Interrupt MCU BS804B/BS808B ® MCU Read Touch Key Status Step1: MCU send command MCU ® BS804B/BS808B Step2: MCU read key status BS804B/BS808B ® MCU Send command to BS804B/BS808B MCU ® BS804B/BS808B SCD Function Summary · BS804B/BS808B Wakes-up or Interrupts MCU When any of the touch keys change state, a pulse will be generated by the BS804B/BS808B device which can be used to wake up or to interrupt an external MCU. The MCU must ensure that its pin connected to the SCD pin is setup as an input to receive this pulse. The pulse width generated by the device is equal to a tSCD/2 period where tSCD is about 76 ms. · MCU reads the touch key status The MCU can send a command to the BS804B/ BS808B device to request the touch key status. The protocol for reading the touch key status is as follows: ¨ The external MCU takes control of the SCD line and first sends three rising edge pulses or more to the BS804B/BS808B within a time of about 152 ms. ¨ The MCU then changes its I/O pin to an input. ¨ The BS804B/BS808B device will then pull the SCD line low, then high, the timings are given by syn- chronise period. This allows the MCU to synchro- nise itself for the data transfer. ¨ The BS804B/BS808B device will then transmit its key status, given by D0~Dn - For the BS804B, the data format is D0~D3. - For the BS808B, the data format is D0~D7. ¨ The MCU can then read the key status taking care to read the data in the centre of the transmitted data pulse. ¨ After the last data bit is transferred the BS804B/BS808B device will return its SCD pin to an input state. The timings associated with the above protocol can be described in multiples of the SCD clock periods. The SCD clock period is about about 76 ms. A certain time is required for the MCU to transmit three or more pulses to inform the device that it desires to read the key status. After this time has elapsed the de- vice will then transmit the data bits, D0~Dn. Device Time BS804B 22 tSCD BS808B 38 tSCD Key Status Read Total Time Each bit of transmitted data corresponds directly to a touch input key. Therefore the status of touch key Key0 is represented by D0, Key1 by D1 and so on. A ²low² bit means that a touch has been detected, a ²high² bit means no touch has been detected. Pin Data Bit Dn Value Key0 D0 1: Key Off 0: Key On Key1 D1 : : : : Keyn Dn · MCU sends commands to BS804B/BS808B device The MCU can send commands along the SCD line to setup the device in different Operating Modes. To do this the externally connected MCU takes control of the SCD line, first forcing it low and holding it low for a time of greater than 8 tSCD cycles. This action will tem- porarily disable the device and enable it to receive the command from the MCU. Any command sent to the device from the MCU will override the original power on configuration setup. The desired Operating Mode to be setup depends upon the number of pulses received by BS804B/ BS808B within a time period, 4 tSCD, as shown in the table. After the programming clock cycles have been transmitted and the SCD line returns high, the device will return to normal operation. Clock Pulses Operating Mode 0~2 Set by external pin 3~6 One-key wake-up 7~10 For test purposes 11~14 Any-Key wake-up >15 Always normal operation BS804B and BS808B SCD Commands t S C D / 2 M C U I N T o r I / O S C D B S 8 0 4 B B S 8 0 8 B I / P O / P Wake-up/Interrupt Pulse to MCU S C D L i n e f r o m M C U N u m b e r o f p u l s e s w i t h i n 4 t S C D s e t s o p e r a t i n g m o d e 1 2 n T A 4 t S C D N o t e : T A > 8 t S C D P e r i o d s SCD Device Setup |
Similar Part No. - BS801B |
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Similar Description - BS801B |
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