14_data_stream

High if s set goes low q goes to logic high q bar to

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Unformatted text preview: when the clock sees a positive edge – if R (reset) goes low, Q goes to zero (Q-bar to logic high) – if S (set) goes low, Q goes to logic high (Q-bar to zero) – holds Q, Q-bar values as long as S, R, high, no matter what happens to D input, provided no clock edge Winter 2008 18 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 74HC74: Dual D-type flop 74HC574 Octal D-flop • Just 8 D-type flops with same clock, no set/reset • Often called a “latch” preserves data input at clock latch” Winter 2008 Lecture 14 19 Winter 2008 20 5 Data Streams 03/04/2008 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 74HC193 Counter MAX232 RS-232 Level-shifter • Powered by 5V • uses charge-pump capacitors to generate ±12V for RS-232 levels • Provides 2 channels of communication – transmit and receive for each • Load input; count up or down; alert when at end Winter 2008 21 Winter 2008 22 UCSD: Physics 121; 2008 Reading • For magnetic stripe stuff, see: – – – – http://en.wikipedia.org/wiki/Magnetic_stripe_card http://money.howstuffworks.com/question503.htm http://stripesnoop.sourceforge.net/faq.html http://stripesnoop.sourceforge.net/devel/phrack37.txt • See data sheets linked via the Lab 9 Parts List Winter 2008 Lecture 14 23 6...
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