Post by thread:[EE] Plugging in an RS232 plug with computer on

It seems to me that I remember hearing somewhere that one should not plug in a device to a PC while the PC is running, where the devices uses an RS232 interface. Does this have the potential for causing damage to either the device or the PC? I know that a USB plug can be inserted or taken out while the PC is running, but have always thought that an RS232 plug should not be. Does anyone know? John

John, You will almost certainly get replies both ways. However, I was on a job in Portugal recently where the customer had blown up the serial driver chip on an embedded CPU which was caused by both the PC and the equipment being switched on. It went along the lines of, finished commissioning using one PC, swapped to customers PC, never worked again and 2 days later I was on a plane. Once bitten eh ?? Dave John Nall wrote: > It seems to me that I remember hearing somewhere that one should not > plug in a device to a PC while the PC is running, where the devices > uses an RS232 interface. Does this have the potential for causing > damage to either the device or the PC? I know that a USB plug can be > inserted or taken out while the PC is running, but have always thought > that an RS232 plug should not be. Does anyone know? > > John

Dave Wheeler wrote: > > You will almost certainly get replies both ways. However, I was on a > job in Portugal recently where the customer had blown up the serial > driver chip on an embedded CPU which was caused by both the PC and the > equipment being switched on. It went along the lines of, finished > commissioning using one PC, swapped to customers PC, never worked > again and 2 days later I was on a plane. Once bitten eh ?? Well, if replies go both ways, then I will choose the safer route. :-) Even better than being once bitten is listening to someone who has been bit before. Thanks. John

John Nall wrote: > Well, if replies go both ways, then I will choose the safer route. > :-) Even better than being once bitten is listening to someone who has > been bit before. I hot plug RS-232 frequently, surely 1000s of times by now. I have never once found that to damage anything when both ends were proper devices. RS-232 is deliberatly specified to handle a decent voltage range, be short circuit proof, etc. The only problem I can see is if the two devices are floating with respect to each other and static electricity builds up between them. Even then that should be OK if the shields are properly connected because they would make contact first. I always make sure the sheild is connected to ground on stuff I build, but you could have a cable that doesn't wire the shield accross. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com

I have also 'hot plugged' many times, however when a £12,000 bit of kit goes pop, has to be shipped back to the UK for repair, I become 'cautious' :-) In the Fire Alarm industry, it is quite common for shields (screens) to only be grounded at one end ( I thought it was normal in most applications to reduce EMC problems). Lightning can do wonderful things when it has a low impedance path. The one that annoys me is when the 0V rail is connected to ground, I have seen professional equipment with a DB9 and pin 5 connected to the shield, causes havoc with Ground Fault monitoring. Dave Olin Lathrop wrote: {Quote hidden}> John Nall wrote: > >> Well, if replies go both ways, then I will choose the safer route. >> :-) Even better than being once bitten is listening to someone who has >> been bit before. > > > I hot plug RS-232 frequently, surely 1000s of times by now. I have never > once found that to damage anything when both ends were proper devices. > > RS-232 is deliberatly specified to handle a decent voltage range, be > short > circuit proof, etc. The only problem I can see is if the two devices are > floating with respect to each other and static electricity builds up > between > them. Even then that should be OK if the shields are properly connected > because they would make contact first. I always make sure the sheild is > connected to ground on stuff I build, but you could have a cable that > doesn't wire the shield accross. > > > ***************************************************************** > Embed Inc, embedded system specialists in Littleton Massachusetts > (978) 742-9014, http://www.embedinc.com

I heard that people with self-built JDM programmer burnt their PC COM port when hotplugging. I heard that some Intel chipset based Motherboards got the ICH4 south bridge burned when user hotplugged USB device. Often the culprit is the cheaper casing used. Regards, Xiaofan http://tw.giga-byte.com/Motherboard/Support/FAQ/FAQ_456.htm The ICH4/5 SouthBridge chipset on my Intel(r) motherboard appears damaged or "burnt". How did this happen? The GIGABYTE Global RMA Service Center has recently become aware of the randomly occurring risk to ICH4/5 SouthBridge chipsets on Intel(r) motherboards to become damaged or "burnt" when a USB device is connected. Please read the following paragraphs to learn more about this issue. Why did this happen? There are three likely causes: 1) Accumulated static electricity from the human body may have been transmitted to the ICH4/5 SouthBridge chipset when connecting a USB device if it has not been "grounded". 2) A connected USB device does not have any static electricity protection. 3) Accumulated static electricity in a front-panel USB port that is not properly "grounded" with the PC casing. Usage Tips Avoid touching the USB connector. Release static electricity within your USB device by touching the USB connector to any metal surface before plugging it into your computer. Use rear-panel USB ports on your PC whenever possible. Use a three-pronged electrical cord to connect a power supply to your PC. Use only approved or certified power supplies.