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I am trying to interface an RS422 to the UART on my MCU. Now, RS422 is differential. So, I understand that I need to have a differential to single ended converter IC. This is followed by a voltage level shifter to match Voh,Vol,Vih and Vil voltage levels of the MCU UART.

Other than this do I need any buffers or protocol convertyers ? The data is sent at standard baud rates of 460800, 230400, 115200, 57600, 38400, 19200, 9600, 4800 bps. Also, the UART standard rates are in baud, right ? How will it impact the bps. Because baud means symbols. For eg 9600baud = 9600x8bps.

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  • \$\begingroup\$ 9600 baud is 9600 bits per second i.e. 9600 x 1 bit. It also includes the start, stop and parity bits so character rate on a 9600 baud interface with 8 bit characters + parity + start + 2 stop bits will be 9600/12 = 800 characters per second maximum \$\endgroup\$ – Icy Oct 28 '15 at 13:15
  • \$\begingroup\$ Ok. But what is baud ? Symbols,right? Now to transmit each symbol we need a min of 1 start and 1 stop bit. So, A symbol sent is a total of 10 bits. This means if 9600 baud wld mean 96000bps. \$\endgroup\$ – Board-Man Oct 28 '15 at 13:19
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    \$\begingroup\$ No, its the other way round 9600 bits per second / 10 bits = 960 characters per second. Baud = bps \$\endgroup\$ – Icy Oct 28 '15 at 13:23
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For an RS422 link you just need the components you describe - usually just a differential line driver and receiver. The data format is identical to RS232 asynchronous format just sent over a differential pair instead of a single wire and earth.

Baud rate is bits per second or bps - character rate is: baud / no of bits per character (including start, parity and stop bis) so an 8 bit character (or symbol) sent with a start bit and a stop bit - no parity will require 8 bits to transmit, so at 9600 baud we can only send 960 characters per second.

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    \$\begingroup\$ Just a nitpick, but RS422 is a physical layer standard only. So you really can use any data standard you want with it. The data format can be entirely determined by the endpoints. \$\endgroup\$ – Ian Oct 28 '15 at 14:37
  • \$\begingroup\$ Close, but bps != Baud. Often this is true, but bps = n × Baud is more accurate, where n ≥ 1. tldp.org/HOWTO/Modem-HOWTO-23.html \$\endgroup\$ – jippie Oct 30 '15 at 18:25
  • \$\begingroup\$ I stand corrected, but for the RS422 physical layer, baud = bps \$\endgroup\$ – Icy Oct 30 '15 at 22:44

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