14_data_stream

# What transmitter number is binary coded in the usual

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Unformatted text preview: with the Checksum? What’ • Transmitter number is binary-coded in the usual sense: 32768 16384 8192 4096 2048 1024 512 256 128 64 32 16 8 4 2 1 1001000000001 10110010001010111110111 button code 0 0 0 0 0 0 0 01 1 0 1 1 0 0 1 0 0 0 1 0 1 0 1 transmitter ID (normal first-packet version) checksum Break data into chunks of 8 bits (bytes) and add up: • Sum is: 1001 00000000 11011001 00010101 11110111 – 32768 + 16384 + 4096 + 2048 + 256 + 16 + 4 + 1 = 55573 – this exactly the number pasted behind the battery • Second packet inverts all the bits to ensure data integrity Checksums provide a “sanity check” on the data integrity Winter 2008 Lecture 14 7 Winter 2008 8 2 Data Streams 03/04/2008 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 A look at the H-ITT Serial Datastream Stereo Remote Control E-button on H-ITT (first of two packets): 01010000110000000001010011011101010100010111101101 • Similar to H-ITT transmitters in principle: – bursts of infrared light carrying digital information – punctuated by delimiters so no long sequences of 1’s or 0’s • – – – – • • Key differences: Serial datastream looks a lot different – signal initiated by a WAKE UP! constant-on burst – pattern that follows is repeated indefinitely until button is released this one allows many zeros or ones in a row delimiters (called start bit and stop bit) bracket 8-bit data (1 byte) in this case, 0’s are positive voltage, 1’s are negative (backwards!) happens much faster than IR: in this case 19,200 bits/sec (baud) • I can never get fewer than three packets… Packet breakdown: – packet is variable in length depending on button – first packet: button number (5 E), with LSB first: 101000 – next three packets are ID, also LSB first within each – last packet is checksum type of verification data packet data packet 2nd data packet Winter 2008 9 Winter 2008 10 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 Sample patterns for data packet POWER 100000000 VOL A Different Code… Code… 000000000 VOL + 010000000 1 110001000 4 001001000 5 101001000 6 011001000 7 – does not use the 01 delimiters like H-ITT did – instead, uses 10 to represent zero, and 1000 to represent 1 – sequence for the 5 button is: 010000 3 • The radio rem...
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## This note was uploaded on 01/30/2014 for the course PHYS 121 taught by Professor Staff during the Winter '08 term at UCSD.

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