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ELM404SM Datasheet(PDF) 2 Page - ELM Electronics |
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ELM404SM Datasheet(HTML) 2 Page - ELM Electronics |
2 / 9 page ELM404 Elm Electronics – Circuits for the Hobbyist www.elmelectronics.com Pin Descriptions 2 of 9 All rights reserved. Copyright 2011 Elm Electronics. Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve reliability, function, or design. VDD (pin 1) This pin is the positive supply pin, and should always be the most positive point in the circuit. Internal circuitry connected to this pin is used to provide power on reset of the internal logic, so an external reset signal is not required. Refer to the Electrical Characteristics section for more information. A (pin 2) This input should be connected to what is normally known as the ‘A’ signal from a rotary (quadrature) encoder. The signal at this pin should lead (ie change state before) the signal at pin 3 when the device is being moved in a clockwise or up direction. An external pullup resistor is required for the encoder (a typical value is 10 K Ω), but no external capacitors are needed (as the internal debounce circuitry provides the filtering). B (pin 3) This input should be connected to what is normally known as the ‘B’ signal from a rotary (quadrature) encoder. The signal at this pin should lag behind (ie change state after) the signal at pin 2 when the device is being moved in a clockwise or up direction. An external pullup resistor is required for the encoder (a typical value is 10 K Ω), but no external capacitors are needed (as the internal debounce circuitry provides the filtering). Clk Invert (pin 4) This input controls the polarity of the pulse at pin 6. If pin 4 is at a low level, the Clk output will maintain a low quiescent level, with the pulses going to the VDD level. If pin 4 is at a high level, then pin 6 will normally be at a high level, with pulses going low (to Vss). This input can be changed at any time. U/D (pin 5) This ‘Up/Down’ output changes with the direction of encoder rotation. For a clockwise movement (the A input appears first, followed by the B), this output will be set high before the CS output (pin 7) is switched low. For counter-clockwise movement, the output will be set low prior to the Chip Select going low. The U/D output does not change state when the CS and Clk pulsing is complete - it remains at the level it was just prior to the CS going low. Clk (pin 6) A ‘Clock’ pulse will be output at this pin 200 µsec after the Chip Select (pin 7) has gone low. The pulse is 200 µsec wide, and is typically used to cause the controlled device to change state based on the level at the U/D pin. The polarity of this output can be changed at any time by changing the logic level at pin 4. CS (pin 7) This output provides a ‘Chip Select’, or enable function. As the shaft rotates, a series of clock pulses are generated at pin 6. Just prior to these pulses appearing, the CS output will go low, and stay at that level until 200 µsec after the Clk pulse is complete. See the Output Waveforms section (on page 7) for more information. VSS (pin 8) Circuit common is connected to this pin. This is the most negative point in the circuit. ELM404DSA |
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