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HCS412 数据表(PDF) 12 Page - Microchip Technology |
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HCS412 数据表(HTML) 12 Page - Microchip Technology |
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12 / 44 page  HCS412 DS41099C-page 12 Preliminary © 2002 Microchip Technology Inc. FIGURE 3-4: SEED CODE WORD DATA FORMAT TABLE 3-4: SEED TRANSMISSION OPTIONS 3.3 Transmission Data Modulation The data modulation format is selectable between Pulse Width Modulation (PWM) and Manchester using the Data Modulation (MOD) configuration option. Regardless of the modulation format, each code word contains a leading 50% duty cycle preamble and a syn- chronization header to wake the receiver and provide synchronization events for the receive routine. Each code word also contains a trailing guard time, separat- ing code words. Manchester encoding further includes a leading and closing ‘1’ around each 69-bit data block. The same code word repeats as long as the same input pins remain active, until a time-out occurs or a delayed seed transmission is activated. The modulated data timing is typically referred to in multiples of a Basic Timing Element (RFTE). ‘RF’ TE because the DATA pin output is typically sent through a RF transmitter to the decoder or transponder reader. RFTE may be selected using the Transmission Baud Rate (RFBSL) configuration option (Table 3-6). TABLE 3-5: TRANSMISSION MODULATION TIMING * Enabling long preambles extends the first code word’s preamble to TLPRE milliseconds. TABLE 3-6: BAUD RATE SELECTION (RFBSL) SEED TMPSD Description 0 0 SEED transmissions permanently disabled 0 1 Limited SEED transmissions (Note 1) - temporarily enabled until the 7 LSb’s of the synchronization counter wrap from 7Fh to 00h 1 0 SEED transmissions permanently enabled (Note 1) 1 1 SEED transmissions permanently disabled (2 key IFF enabled) Note 1: Refer to Table 3-1 for appropriate button activation of SEED transmissions. QUE 2 Bits CRC 2 Bits VLOW 1-Bit BUT 4 Bits SDVAL3 12 Most Sig Bits S2 S1 S0 LC0 Note: SEED transmissions only allowed when appropriate configuration bits are set. SDVAL2 16 Bits SDVAL1 16 Bits SDVAL0 16 Least Sig Bits Q1 Q0 C1 C0 LSb 69 Data bits Transmitted LSb first. MSb Shaded data included in CRC calculation Period PWM Manchester Units Preamble 31* 31* RFTE Header 10 4 RFTE Data 207 142 RFTE Guard 46 31 RFTE RFBSL1:0 CWBE PWM RFTE Manchester RFTE Transmit... 00b X 400 µs 800 µs All code words 01b 0 200 µs 400 µs All code words 1 200 µs 400 µs Every other code word 10b 0 100 µs 200 µs All code words 1 100 µs 200 µs Every other code word 11b 0 100 µs 200 µs All code word 1 100 µs 200 µs Every fourth code word |
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