An error detecting method none even odd mark space

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Unformatted text preview: +5 to +15 V (usually ~12 V) on transmit • +3 to +25 V on receive • old stuff often used 7 – the dead zone is from 3 V to +3 V (indeterminate state) – Parity: An error detecting method: None, Even, Odd, Mark, Space – Stop bits: number of stop bits on each byte; usually 1. • Usually used in asynchronous mode • Rarely 2 or (more rarely) 1.5: just a minimum wait time: can be indefinite – so idles at 1 2; start jumps to +12; stop bit at 12 – since each packet is framed by start/stop bits, you are guaranteed a transition at start – parity (if used) works as follows: • even parity guarantees an even number of ones in the train • odd parity guarantees an odd number of ones in the train stop 2 stop 1 parity idle bit 6 bit 5 bit 4 bit 2 bit 1 bit 0 start Winter 2008 bit 3 9600, 7E2 idle 5 to 1 5 V (usually about 12 V) on transmit 3 to 25 V on receive slide courtesy E. Michelsen 13 Winter 2008 14 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 GPIB (IEEE-488) Data Acquisition • An 8-bit parallel bus allowing up to 15 devices connected to the same computer port – addressing of each machine (either via menu or dipswitches) determines who’s who – can daisy-chain connectors, each cable 2 m or less in length • Extensive handshaking controls the bus – computer controls who can talk and who can listen • Many test-and-measurement devices equipped with GPIB • A PCI-card for data acquisition is a very handy thing • The one pictured at right (National Instruments PCI-6031E) has: – – – – – 64 analog inputs, 16 bit 2 DACs, 16 bit analog outputs 8 digital input/output 100,000 samples per second on-board timers, counters • Breakout box/board recommended – common means of controlling an experiment: positioning detectors, measuring or setting voltages/currents, etc. • Can be reasonably fast (1 Mbit/sec) Mbit/sec) Winter 2008 Lecture 11 15 Winter 2008 16 4 Computer Interface 02/21/2007 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 CAMAC • This somewhat old interface provides a “crate into crate” which one slides modules that perform specific tasks – – – – – – A/D conve...
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