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Data communication circuits page ( 30 ) :

Cable wirings

Serial communication conversion circuits

Serial communication isolation circuits

Galvanic isolation eliminates problems arising from disparate potentials between terminals.

Serial interface protection

Serial interface application notes

Serial communication data generation and receiving

  • Synchronizing controller detects baud rate - A simple and inexpensive implementation using an eight-pin 12C508 controller (Microchip Technology, Chandler, AZ) provides both bit-rate detection and a synchronous, appended-clock output from an asynchronous input-data stream.
  • Use a PIC for automatic baud-rate detection - Automatic baud-rate detection is desirable in many applications. Microchip's (www.microchip.com) standard USART module that the company embeds in most of its PIC microcontrollers lends itself to a simple and easily implemented automatic baud-detection scheme. This example is designed for PIC18FXX2 in mind.
  • Use power line for baud-rate generation - One cost-saving measure associated with 8-bit embedded microcontrollers is to use a resistor-capacitor oscillator. These RC oscillators are inexpensive, but the trade-off is low stability with temperature and voltage. In these cases, you can find a low-frequency, stable clock source and use it to calibrate a baud-rate generator or event timer. One source of a low-frequency, stable clock is the line voltage. This voltage is a good source 50- or 60-Hz frequency that you can easily interface to the microcontroller's 16-bit timer. By counting CPU cycles for a half cycle of the external clock, you can determine the frequency of the microcontroller's internal RC oscillator and calibrate the baud rate.

Logic signal level translations

  • Circuit converts between TTL and shifted ECL
  • Logic Family Voltage Translation - how to translate between TTL, 74xx, CMOS, ECL, PECL, Low Voltage TTL, LVTTL, etc.
  • Simple RS-232 receiver - simple one transistor RS-232 level to TTL level converter
  • TTL to RS-232 interfacing
  • Two transistors form bidirectional level translator - illustrates a translation from 5 to 3V, but it can accommodate almost any other voltage levels, provided the logic-low levels are equal (usually 0V), translation from 1 to 100V are possible although slow.
  • Two-transistor circuit replaces IC - Linear Technology's recently introduced LTC4300 chip buffers I2C clock and data lines to and from a hot-swappable card. This task is difficult because the IC must work bidirectionally, meaning that you can simultaneously and actively drive both sides. However, as is sometimes the case, you can replace a complicated circuit by a simple one without much loss of performance. For example, transistors and resistors replace the entire IC. Two npn transistors, connected head-to-head, form the heart of the circuit. The two-transistor circuit offers the additional benefit of acting as a level translator between two logic levels, for example 3.3V and 5V.

Transmission line interfacing

Modulation, demodulation and coding

Other circuits

  • Synchronizing controller detects baud rate - a simple and inexpensive implementation using an eight-pin 12C508 controller (Microchip Technology, Chandler, AZ) provides both bit-rate detection and a synchronous, appended-clock output from an asynchronous input-data stream

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