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Digital Electronics and Computer Interfacing

Digital Electronics and Computer Interfacing. Tim Mewes 7 . Computer Interfacing – Serial communication. 7 Serial communication. In serial communication data is send one bit at a time Advantages compared to parallel communication : less cables required

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Digital Electronics and Computer Interfacing

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  1. Digital Electronics and Computer Interfacing Tim Mewes 7. Computer Interfacing – Serial communication

  2. 7 Serial communication In serial communication data is send one bit at a time Advantages compared to parallel communication: • less cables required • Signal delay between cables not an issue • crosstalk between cables not an issue Main disadvantages: • Speed • Getting it to work… Digital Electronics and Computer Interfacing

  3. 7.1 Serial communication via RS-232 RS-232 (recommended standard 232) 1969: defines • signal levels (up to 25V) • signal rate (Baud or bits/s) • connectors DB-25 (recommended) however DE-9 is most common • Does not define: • Character encoding (ASCII) • actual transmission rate • start/stop bits, data bits, parity Digital Electronics and Computer Interfacing

  4. 7.1 Serial communication via RS-232 Communication: Here: • 1 start bit (signals the receiver that data follows) • 8 data bits • no parity bit (used to check for incorrect transmission, could be even or odd) • 1 stop bit (indicates that data transmission is over) if no further data follows line remains high Digital Electronics and Computer Interfacing

  5. 7.1 Serial communication via RS-232 Thus before communication can take place sender and receiver need to “decide” on: • Transmission speed (baud rate) • Number of data bits typically 8 • Parity (none, even or odd) • Number of stop bits (1 or 2) • Flow control “handshaking” (none, hardware, software (XON/XOFF)) • Check the manual of the device! Digital Electronics and Computer Interfacing

  6. 7.1 Serial communication in LabVIEW Write command Check manual Wait – if needed • Configure port first • VISA resource name: COM1/COM2 • baud rate (9600 or 2400, 4800, 7200 etc.) • data bits (8 or 7 are most common) • parity (none most common) • stop bits (1, 1.5 or 2) • flow control (none most common) Read response Check manualwhat to expect End session Cleanup! Digital Electronics and Computer Interfacing

  7. 7.2 Serial communication problems • Check that LabVIEW settings match those in manual • flow control is often source of problems in particular hardware flow control – it is just not implemented reliably in many devices • PIN assignment differs between DTE (Data Terminal Equipment) and DCE (Data Circuit-terminating Equipment) • PIN assignment Minimal 3-wire connection Minimal 5-wire connection with flow control Digital Electronics and Computer Interfacing

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