Simple -How to wire Arduino to temp controller with RS485

hey guys,

so trying temp values out of solo 4848 temp controller via modbus rs-485. anyways, should simple possible , don't need else connected, want working first.

i using linksprite rs485 shield v2.1 https://www.sparkfun.com/products/12965

of few tutorials have seen online, none different 1 provided website.
here http://learn.linksprite.com/arduino/shields/tuotorial-of-using-rs485-shield-v2-on-arduino/
most tutorials 2 arduinos communicating or similar.

i'm using arduino duemilanove switching sparkfun redboard soon.

in short, how wire temp controller arduino?
i need make sure getting right data , using usb power computer now, need use softwareserial.

i want understand wires can , cannot go , why. have few basic electric questions build knowledge base. in tutorial link posted, under wiring diagram tab, can see 2 arduinos connected 2 wires rs485 ports yet description still mentions connecting other things well. here text wiring diagram

"left rs485 module h2 485-a -> right rs485 module h2 485-a

left rs485 module h2 485-b  -> right rs485 module h2 485-b

left rs485 p1 -> 3.3v  right rs485 p1-> 3.3v

left rs485 p2 -> tx_ctrl  right rs485 p2->  tx_ctrl

left rs485 d2 -> tx  right rs485 d2 -> tx

left rs485 d3-> rx  right rs485 d3->  rx"

what reasoning 3.3v connection , tx_ctrl connection etc? rs485 uses 2 wires, why necessary? specific communicating 2 arduinos? in case have 2 wires coming temp controller, need else modbus rs485 work me?

here other base questions curious about,

1. on linksprite shield shown below, difference between rs485 ports labeled h1 , h2? shield have 2 ports communicate with, if 1 enough? or supposed work together?

2. pin/port thing labeled p1, saying 5v , 3.3v, relevant me?

3. pin/port labeled p2? says d9_ctrl , tx_ctrl. seems weird me labeled p1 , p2 aren't inversely labeled having similar functions. basically, when 1 says tx_ctrl, why doesn't other rx_ctrl, why there tx_ctrl , not rx_ctrl, 5v , 3.3v (volts know) supposed receiving voltage in between values or?

even if don't have specific question something, if seems should know related, please tell me! seem missing big concept of circuits or rs485 connection?

sorry spamming beginner questions , info,

remember trying communicate temperature device, not arduino should mean circuit lot less complicated, correct?

so far thing have done believe correct put black wire (negative) shield's h1 rs485 b , red wire (positive) rs485 port. since need use softwareserial, how tell arduino ports communicate with? rs485 shield default using pins 0 , 1 (tx , rx) serial ports?

i feel lot of stuff stupid easy questions or common knowledge, new circuits , rs485 apologize if questions entry level or don't make sense.

i have attached photo of rs485 shield using quicker reference.

i appreciate , can give.

thank you! -dillon

 i not familiar shield wont there.

p1 determines operating voltage. can either 3.3 or 5v arduinos use 5v should check temp controller uses also.

tx_ctrl used tell shield if should transmitting or receiving.

you not using softwareserial.

 modbus communication protocol used controller
will need use on arduino.

modbusmaster library

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