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MAX11041 Datasheet(PDF) 8 Page - Maxim Integrated Products |
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MAX11041 Datasheet(HTML) 8 Page - Maxim Integrated Products |
8 / 17 page Keypress Detection and Debounce At power-up, the MAX11041/MAX11042 begin to moni- tor the SENSE input for keypresses. When the MAX11041/MAX11042 detect a keypress at SENSE, they attempt to debounce the SENSE input. After suc- cessful debouncing of the input, the corresponding keypress result is inserted into the FIFO. In addition, INT goes low to signal a keypress to the µP. Keypress FIFO and Time Duration After detecting and debouncing a key, the decoded key is stored in one byte of the 8-word FIFO. A 7-bit internal timer starts counting the duration of the key- press (one count = 32ms) and the result is stored after each increment in another byte of the 8-word FIFO. The 8th bit in the time duration byte is an overflow bit that is set when the count reaches 128. After the count reaches 128, the 7-bit timer rolls over to 0 and contin- ues to count while the 8th bit becomes set and stays set until the associated FIFO entry is cleared. For key- press durations longer than 8.16s, see the Extended Keypresses section. When the device detects another change in resistance at SENSE (either by key release or another keypress), the count resets and the FIFO begin recording the next keypress/duration. This allows the 8-word FIFO to store time duration and key-type information for up to four keypresses and releases. When the FIFO is full and a key is pressed, the oldest keypress information in the FIFO is written over. Writing to the power-down bit (bit 6) in the control register or bringing SHDN low clears the FIFO to its power-on-reset (POR) state. Wired Remote Controllers 8 _______________________________________________________________________________________ ➂ ➁ ➀ ➃ 1. DEBOUNCED KEYPRESS STORED IN FIFO AND INT GOES LOW, DURATION TIMER STARTS. 2. PROCESSOR READS FIFO AND INT GOES HIGH. KEY TYPE AND CURRENT KEYPRESS DURATION TIME SENT. FIFO IS NOT CLEARED. 3. KEYPRESS RELEASES AND INT GOES LOW. KEY TYPE AND FINAL KEYPRESS DURATION TIME STORED IN FIFO. 4. PROCESSOR READS THE FIFO AND INT GOES HIGH. KEYPRESS INFORMATION STORED IN FIFO FROM STEP 3 IS CLEARED. KEY TYPE TIME TIME VINT Figure 3. Reading the FIFO While the Key is Still Pressed ➂ ➁ ➀ TIME TIME VINT 1. DEBOUNCED KEYPRESS STORED IN FIFO AND INT GOES LOW. DURATION TIMER STARTS. 2. KEYPRESS RELEASES. KEY TYPE AND KEYPRESS TIME DURATION INFORMATION STORED IN FIFO. 3. PROCESSOR READS FIFO COMPLETELY AND INT GOES HIGH. PREVIOUS KEYPRESS INFORMATION CLEARED. KEY TYPE Figure 4. Reading the FIFO After the Key is Released BIT NAMES CHIP ID I7 I6 I5 I4 I3 I2 I1 I0 MAX11041 0 0000 000 MAX11042 0 0000 001 Table 3. Chip ID Data Format |
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