Download Data Streams in Physics 121: Transmission and Bit Sequences and more Lecture notes Experimental Techniques in PDF only on Docsity!
Winter 2011 UCSD: Physics 121; 2011 2
1 st^ data packet 2 nd^ data packet
Winter 2011 UCSD: Physics 121; 2011 3 Transmitter 55573 sends an “A” Transmitter 55573 sends a “B”
first packet
second packet
first packet
second packet
Winter 2011 UCSD: Physics 121; 2011 4 Differences are minor, showing up only near beginning & end We will represent “high” states (light on) as 1’s, and lows (off) as 0’s Notice standard widths: choices are single- or double-width
(both for the zeros and the ones)
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Sequence starts out: 01101001001101001001001001… Notice the 01 delimiters: 01101001001101001001001001 … This gives the signal its choppy appearance (never see 3 1’s or 0’s in a row) Actual data appears between delimiters: 1’s look fat, 0’s look skinny Resulting bit-sequence for A signal (both packets) is:
button code transmitter ID (normal and inverted) checksum
end delimiter
Winter 2011 UCSD: Physics 121; 2011 6 B A C D E 1001 → 001 → 1 1010 → 010 → 2 1011 → 011 → 3 1100 → 100 → 4 1101 → 101 → 5
first bit always 1
<< (^1110) → 110 → 6 Winter 2011 UCSD: Physics 121; 2011 7 0 0 0 0 0 0 0 0 1 1 0 1 1 0 0 1 0 0 0 1 0 1 0 1
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button code transmitter ID (normal first-packet version) checksum
Break data into chunks of 8 bits (bytes) and add up: 1001 00000000 11011001 00010101 11110111 Checksums provide a “sanity check” on the data integrity
Winter 2011 UCSD: Physics 121; 2011 13
zeros ones mixed traditional Winter 2011 UCSD: Physics 121; 2011 14
track 3
track 1
track 2
data direction
Winter 2011 UCSD: Physics 121; 2011 15 --Data Bits-- Parity! b1 b2 b3 b4 b5 Character Function! 0 0 0 0 1 0 (0H) Data! 1 0 0 0 0 1 (1H) "! 0 1 0 0 0 2 (2H) "! 1 1 0 0 1 3 (3H) "! 0 0 1 0 0 4 (4H) "! 1 0 1 0 1 5 (5H) "! 0 1 1 0 1 6 (6H) "! 1 1 1 0 0 7 (7H) "! 0 0 0 1 0 8 (8H) "! 1 0 0 1 1 9 (9H) "! 0 1 0 1 1 : (AH) Control! 1 1 0 1 0 ; (BH) Start Sentinel! 0 0 1 1 1 < (CH) Control! 1 0 1 1 0 = (DH) Field Separator! 0 1 1 1 0 > (EH) Control! 1 1 1 1 1? (FH) End Sentinel! Winter 2011 UCSD: Physics 121; 2011 16
Winter 2011 UCSD: Physics 121; 2011 17 Winter 2011 UCSD: Physics 121; 2011 18
R
S
Q
Q
D
CLK
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