RS232 intermitted issue  - Page 1
Forum section: electronics / beginners

author: tzc24
author_rank: Newbie
timestamp: April 26, 2024, 07:06:37 am
content: Hi,I connected the DP9 with RS232 to communicate to the PPMC board through TeraTerm software. In order for me to configure my PPMC board i would need to choose the Boot from 0xfff00000 <P1000 vxWorks>? but due to this is not the first priority so i need to press"n" from my PC to PPMC board trough the RS232 protocol but when i press "n" sometime the PPMC board able to get respond but sometime it is not. If anyone had encountered the similar issue before?Attached with the TeraTerm screenshot.Kindly advice on this.Thank you.Best Regards,tzc

author: xvr
author_rank: Frequent Contributor
timestamp: April 26, 2024, 07:00:44 pm
content: Check the voltage level on TX pin of PC. RS232 demand negative voltage there (+/- 12V as I remember). Some PC will not provide negative at all and reduced positive (about 5-10V). Not all RS232 receivers accept this.

author: aliarifat794
author_rank: Regular Contributor
timestamp: April 27, 2024, 03:11:15 pm
content: You can try a different terminal emulation software, such as PuTTY or HyperTerminal, to see if the issue persists.

author: tzc24
author_rank: Newbie
timestamp: April 27, 2024, 11:49:48 pm
content: I had checked all the tx voltage there are no abnormality found.

author: tzc24
author_rank: Newbie
timestamp: April 27, 2024, 11:52:04 pm
content: Quote from: aliarifat794 on April 27, 2024, 03:11:15 pmI have tried different terminal and unfortunately all come out with the same output.

author: m k
author_rank: Super Contributor
timestamp: May 01, 2024, 04:42:09 pm
content: What kind of cable you have?Could be a transient if pins are not connected but still in use.Or ground current if both ends of cable shield are connected and potential difference is enough.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: May 01, 2024, 07:33:36 pm
content: Make sure your flow control is configured correctly.This could be caused by software flow control not being turned on. So if it's required, then that's probably your problem.Also make sure bits-parity-stop settings are correct.

author: CaptDon
author_rank: Super Contributor
timestamp: May 02, 2024, 12:47:40 am
content: I am not sure if your board needs only three wires, Pin 2,3 and 5 for TX, RX and ground OR if it wants all 9 pins available for things like CTS, RTS and so forth. If flow control is used it is probably hardware implemented and not software implemented. Software X-On / X-Off went out with the dinosaurs but CTS / RTS is still popular with the RS-232 signalling. 99% of RS-232 devices will work fine with +/- 5 volt signalling levels and probably 80% will work with levels as low as +/- 3 volts. Fast baud rates are evil with marginal cables and marginal signal levels!! 115K Baud gets iffy in probably 50% of all the stuff I have had to service. Can you get both ends to slow down to 38.4K Baud? This will often be more reliable.

author: Retirednerd2020
author_rank: Regular Contributor
timestamp: May 02, 2024, 04:54:27 pm
content: Serial configuration as others have suggested, and:Look at the serial signals both ways with an oscilloscope and measure the bit rate both ways. Do they match? I have seen bad DUT clock (mis-configured or wrong crystal or other problem) cause serial issues.With a short cable ~3-12 Feet (1-4 Meters) , I've not had issues with 115,200 Baud if the bit-rates are within/near what they should be.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: May 02, 2024, 08:41:52 pm
content: Quote from: CaptDon on May 02, 2024, 12:47:40 amBut it's still widely used in point-of-sale systems. So you can't pretend it doesn't still exist. Why use it? It makes it easy to have printers a long distance from their terminal. Since you only need TX, RX, and GND.