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EDE-1144 Datasheet(PDF) 4 Page - List of Unclassifed Manufacturers |
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EDE-1144 Datasheet(HTML) 4 Page - List of Unclassifed Manufacturers |
4 / 7 page EDE1144 Keypad Encoder IC Page 4/7 OVERVIEW OF OPERATION Table One of the previous page illustrates the data that is output upon each keypress. The following sequence is initiated upon each keypress, and is repeated if the key is held: 1. Keypress is detected 2. One scan cycle is performed 3. Parallel Outputs (D3..D0) are latched with the appropriate value 4. Data Valid signal is activated (pulled low) 5. Beeper (1KHz square wave) is activated for 45mS 6. Serial data is transmitted This entire cycle takes 50mS (regardless of Baud rate selected). If a key is held longer than the autorepeat delay of 660 mS, the cycle is repeated again at a rate of 5 times per second. The following timing diagram illustrates the above sequence: 0ms 10ms 20ms 30ms 40ms 50ms Keypress Parallel_Outputs Data_Valid_Output Serial_Output Beeper_Output D3..D0 latched with appropriate value 45mS 50mS 1uS (Multiple transitions are due to contact bounce) (Square wave is not to scale) Once a key is pressed, any additional closures (bounce) of that contact, or of any other contacts are ignored for 50mS, during which several signals are output by the EDE1144. First, the parallel outputs D0..D3 (Pins 6-9) are latched with the appropriate keypress value. One microsecond later, the Data Valid Output (Pin 17) goes low, indicating that there is valid data on the parallel output pins. Following this, the Beeper Output (Pin 18) pulse stream is generated for 45mS, providing auditory confirmation to the keypad operator that a key has been pressed. Finally, the RS-232 Output (Pin 1) transmits the keypress data at the Baud rate selected by the Baud rate input select (Pin 2). After this, a variable (determined by Baud rate chosen) delay period is waited to make the entire process to last precisely 50mS. If a key is held longer that the autorepeat delay of 660mS, the outputs are cleared and this entire process is repeated every 204mS until the key is released by the operator. |
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