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Quorten Blog 1

First blog for all Quorten's blog-like writings

Here is a quick summary of various means for serial communications and the resulting pin counts.

Different variations of serial communications connectors.

  1. SPI is the simplest type because it can connect straight to a shift register. How many pins? Typically 7 to 8: Ground, 3.3 V, 5 V (optional), RESET, Slave Select, CLOCK, MOSI, MISO.

    If we omit RESET and use power-cycling for RESET instead, assuming the receiver has a power-on-reset circuit, then we can go with only 6 pins.

  2. Asynchronous serial communications. Eliminating the separate clock signal allows for only 5 pins: Ground, Power, Data Terminal Ready (DTE), Transmit, Receive.

    To get to 4 pins, DTE can be eliminated by assuming a bus protocol that transmits that information “in-band,” i.e. software flow control rather than hardware flow control.

  3. Asynchronous serial communications, half-duplex. 3-state logic and state tracking is used to perform transmit and receive on the same conductor. 3 pins.

  4. Multiplexed power and data transmission, “powerline communications.” Data transmission is modulated on the power line. 2 pins.

  1. Single-wire earth return, half-duplex powerline communications. This is technically not feasible in portable hand-held electronics since they are low-voltage and may have no earth return path, especially when they are airbourne.