RS232 serial Data not sending

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Joined: Mon Aug 10, 2015 1:37 am

RS232 serial Data not sending

Post by madScientist001 » Mon Aug 10, 2015 2:58 am

Hello to all!

I just got my first arduino uno board 2 months ago and have been progressing quite well until now. I've spend the last month trying to troubleshoot why my arduino board is not sending serial commands over RS232 to a card dispenser device. The card dispenser uses RS232 to control it. I have a arduino Uno and a linksprit RS232 shield with a MAX3232 chip. Starting simple I'm just trying to code the Eject Front command shown below under command structure. The device receives ASCII codes. According to the device manual it reads:

Communication Protocol:
Baud rate(BPS): Can be set by controller(Default at 9600BPS)
Communicate Mode: Asynchronous communication
Transmit mode: Half duplex
Data frames structure: Start bit: 1bit
Data bit:8bits
A Check Bit: No
Stop Bit:1bit

Command Structure:
Eject Front command
<STX> : 0 2 H , Frame start
<ETX> : 0 3 H , Frame end
<BCC>: <STX> ⊕ O ⊕ O ⊕ O ⊕ O ⊕ <ETX> ,Block checkout

I've written the code below in HEX only because I'm confused on how to send the start and end frame in ASCII. Also because I listened to the communication between the device and PC and matched the HEX commands but the code send should be ASCII according to the manual.

#include <SoftwareSerial.h>

SoftwareSerial deviceSerial(6, 7); // RX, TX

void ejectFront();

void setup() {

void loop() {

void ejectFront() {

Thank you for taking your time to read this.

Posts: 64
Joined: Tue Aug 07, 2012 2:41 am

Re: RS232 serial Data not sending

Post by effgee » Tue Sep 22, 2015 6:41 am

why use softwareserial when you have 4 hardware uarts ?

Hardware serial will always be more reliable, some devices are fussy about exact timings, which software serial can't provide, especially depending what else your program is doing.

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Location: Melbourne, Australia

Re: RS232 serial Data not sending

Post by angusgr » Thu Sep 24, 2015 4:55 am

This looks like it should work to me, at a glance. Can you ask the card dispenser vendor for any feedback on the code?

Regarding soft vs hard serial, I think SoftwareSerial is the right approach if you're using an 'uno'-compatible board. An Arduino Mega compatible (like the EtherMega) has 4 UARTs but Uno-compatible (like Freetronics Eleven) does not.

I'm going to move this thread out of the EtherMega forum though, as I think that's what caused the confusion.

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