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RS485 Shield V2 - Raspberry Pi
Our friends over at LinkSprite have made this nifty little RS485 Shield V2 for the Raspberry Pi, now you will be able to have a communication port for your field bus directly connected to your RPi! Even though the RS485 is sometimes thought as an "archaic" protocol, it will allow up to 32 devices to communicate through the same data line over a cable length of up to 4,000ft with a maximum data rate of 10Mbit/s. Those aren't bad numbers!
This shield comes pre-assembled so all you will need to do is just snap it right onto your Raspberry Pi and get programming. The RS485 Shield V2 is compatible with Raspberry Pi B and B+.
Note: The shield has an unpopulated footprint for a DB9 connector. Check below if you need to add the connector. Otherwise you can use the screw terminals.
- Schematic
- Datasheet (MAX481CSA)
- User Guide
- Product Wiki
RS485 Shield V2 - Raspberry Pi Product Help and Resources
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Customer Reviews
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Fail on the TXEN - it should be driven by software when you know the transmit has finished instead of trying to guess with some nasty bodge using TXD. 485 can run anything from 9600 to 4Mbaud so you just can't guess like that. Also no ground on the terminal block. Though 485 is differential, running it without a ground ref can be asking for trouble
As plagued the first version, this version has the RE and DE controlled by the Tx line. How is this supposed to work? I don't see a decay capacitor on the gate of Q1, so best I can tell, the MAX485 will only transmit zeroes (when tx is low), and be in receiving mode when trying to transmit ones (when tx is high).
You are correct; this is not a true RS485 implementation. It's more like SAE J1708, which is an OR-tied differential bus that runs at 9600 baud.
When can it back? I waited it so long time. It stated that this product mat come on July 22 first, 29th next. Please check it out.
Quick comment about the unpopulated connector. Common usage calls it a "DB-9", but that is technically incorrect. The D-series connectors were first invented by ITT Cannon and the second character of the name is the shell size. The "B" shell size is what is normally seen on 25-pin D connectors. The shell on 9 pin connectors is actually the "E" size shell, so the proper name is "DE-9".
Instead of paraphrasing, I'll just quote Wikipedia on the most likely origin of this error:
"However, this naming pattern is not always followed. Because personal computers first used DB-25 connectors for their serial and parallel ports, when the PC serial port began to use 9-pin connectors, they were often labeled as DB-9 instead of DE-9 connectors, due to an ignorance of the fact that B represented a shell size. It is now common to see DE-9 connectors sold as DB-9 connectors. DB-9 nearly always refers to a 9-pin connector with an E size shell."
That said, because of usage, keep on calling it a "DB-9", and remember that almost always "DB-9" == "DE-9" in case someone actually uses the correct terminology.
But just remember this little bit of connector lore to tell the grand-kids around the camp fire.
Is it possible to stack these boards to get 2 458 ports?
Broken link on the schematic
Well that was weird. Should be fixed now!