RS-485_Breakout

Other Miscellaneous
1

  1. The diagram does not show the RTS connection to the connector JP9.

  2. The U2 chip does not have pin numbers 1…8 and does not have the brand name SP3485.

  3. The VCC voltage change limits are not specified, for example 3.3V or 3.3-5V.

    RS485
    RS485599×316 40.2 KB

2

1 - Good point, it’s not shown in the schematic but it’s pin 4 on JP9
2 - If you cross reference the data sheet, pin numbers show up there, & looks like the schematic shows sparkfun’s internal part number.
3 - From the “features” section on the product page:

  • Operates from a single +3.3V supply Interoperable with +5.0V logic

It looks like this is a pretty early product from sparkfun from before they refined their schematics.

3

Thanks for the answer. And how would you comment on the non-standard resistor R4 220 Ohm? According to the RS-485 standard, it should be 120 Ohm to match the wave resistance of the cable.

4

Sorry, don’t know why they chose that value but i have used these breakouts on 100’s of feet of random wire I had laying around and they worked fine.

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