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MCS3142-I/ST 数据表(PDF) 25 Page - Microchip Technology |
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MCS3142-I/ST 数据表(HTML) 25 Page - Microchip Technology |
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25 / 37 page  2014 Microchip Technology Inc. DS40001747A-page 25 MCS3142 7.0 DEVICE OPERATION 7.1 LED Operation The LED pin will be driven low periodically while MCS3142 is transmitting data. This output is designed to drive an external LED with an appropriate current-limiting resistor. The duty cycle varies between normal operation and a low battery condition (see Figure 7-1). Refer to Section 5.4 “Battery Level and Low Battery Flag” for details on low battery conditions. FIGURE 7-1: LED OPERATION 7.2 Button Configuration MCS3142 allows all combinations of the four buttons to be individually assigned to an encoder. Each combination can also be assigned to transmit either a typical code word or a seed word for the assigned encoder. This gives complete flexibility to the system designer. The button configuration is stored as two 16-bit words. Each bit in a Configuration Word represents one particular combination of active/inactive states of the buttons. The bit is determined by taking the four switches as one 4-bit value, with S0 being Least Significant, followed by S1, S2 and S3. For example, the Configuration bit corresponding to S1 and S2 active (or binary ‘1’) and S0 and S3 inactive (or binary ‘0’) is given by . Configuration bit zero is considered “do not care” as it represents all buttons in their inactive state, which is a special condition for the encoder. One Configuration Word controls the encoder assignment, with a ‘0’ representing the Classic KEELOQ encoder and a ‘1’ representing the Ultimate KEELOQ encoder. The second word controls transmission type, with ‘0’ representing a typical transmission and ‘1’ representing a seed transmission. Because the MCS3142 memory is byte-oriented, each 16-bit Configuration Word is stored as two 8-bit bytes in “little endian” order. See Table 3-19 for encoder assignment and Table 3-20 for seed assignment. Table 7-1 may assist in calculating configuration values by iterating all button state combinations in the order in which they correspond to Configuration bits. In this worksheet, each column represents a specific set of states of the buttons, which in turn represents one bit in the Configuration Word. A stated button, for example S0 or S1, represents that button in its active state. A hyphen in place of a switch label represents that switch in its inactive state. Once all states have been assigned an encoder and a transmission type, the result can be examined as a 16-bit binary number and transcribed into the configuration values. Rev. 20-000012A 9/25/2013 S[3210] VDD > VLOW LED VDD < VLOW LED TLEDON TLEDOFF TLEDON = 200 ms TLEDOFF = 800 ms TLEDOFF TLEDON TLEDON = 200 ms TLEDOFF = 200 ms S3S2S1S0 0110 2 6 == ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ BTN CFG ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ = Button Configuration Byte 1 Button Configuration Byte 0 LSb * 0 = Classic KeeLoq, 1 = Ultimate KeeLoq Seed CFG ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ = Seed Button Configuration Byte 1 Seed Button Configuration Byte 0 LSb * 0 = Typical transmission, 1 = Seed transmission TABLE 7-1: BUTTON CONFIGURATION WORKSHEET S0 — S0 — S0 — S0 — S0 — S0 — S0 — S0 — S1 S1 — — S1 S1 — — S1 S1 — — S1 S1 — — S2 S2 S2 S2 — — — — S2 S2 S2 S2 — — — — S3 S3 S3 S3 S3 S3 S3 S3 — — — — — — — — |
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