GPIO and Serial IO

Dear all,

A very basic question, i guess ...

what are the differences between serial IO and GPIO (General Purposes) IO ?




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GPIO generally means individually toggled I/O lines. The classic is a 8-bit I/O port where you can control the 8 bits of the port.

Serial I/O implies that only 1 bit is controlled. The classic is an 8-bit I/O port where the bits loaded into the port and put into a shift register which then shifts the data out on one I/O line. Data coming in on the line (or another) does the opposite - the data on the I/O line is clocked into the shift register which can then be read from the 8-bit I/O port.

You can implement serial I/O using GPIO by toggling the bits via a program.

Reply to
Gary Kato

The other normal difference is the signal levels on the pins. A GPIO port will usually be TTL or CMOS levels, while a serial port has RS-232 or 422 drivers. But, I have seen a full serial I/O port implemented in software on a GPIO port. Two pins for data, the rest for modem control lines. There were multiple drivers and receivers on each line, so it could be used either way.

Bob McConnell N2SPP

Reply to
Bob McConnell



Serial I/O is not just RS232 it is all formats that send 1 bit at a time. I2C, USB, SMBus, DQ, MSIO, 1 wire, ect. They fall into 2 groups synchronous (clk and data) and asynchronous (data line only)

GPIO on a cpu are usually the non special purpose pins. The are can be used to read from or write to the out side word (outside the CPU anyway). The can be used for parallel, bit banged serial, or individual control pins.

Reply to
Neil Kurzman

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