Re: Serial port connectivity issues

Christopher Erickson

There are some other variables that can play into computer reliability when doing wired inter-device communications.  This is regardless of whether the communications involves USB, serial, Ethernet, Firewire, Thunderbolt, PCI, SATA, EIDE or whatever. 
* 16 and 32-bit drivers installed on a 64-bit OS.  This almost always results in tears and corrupted registries.   A good registry repair and cleaner app usually helps.  For some people, scrubbing the drive and re-installing the OS was the only thing that worked 100% of the time.
* Registry corruption caused by installing certain non-64-bit apps.  Messy problem to solve once created.  A good registry repair and cleaner app usually helps. 
* ESD.  Never plug a communications cable into a device/PC and then let the other end lay on a carpet or floor in a cold/dry environment.  Just the act of walking past the loose end of the cable can cause enough static electricity buildup to destroy interface electronics.  
* Ground loops.   These aren't all that common but when they exist, they can destroy or lock-up electronics or create crazy noise problems for cameras.
* Legacy apps that are designed to synchronize with certain smartphones, GPS's and PDA's.  They often grab or regularly-poll serial or USB ports, looking for a device to sync with.  That can prevent or disrupt communications with other devices.
* Poor or incomplete 16550 UART emulation.  This is specific to USB-to-Serial adapters.  The 16550 UART (Universal Asynchronous Receiver/Transmitter) is the standard serial interface chip found in computers with regular serial interfaces.  It is descended from the 16450 and the even-older 8250 UART chips.  The 8250 UART was first used in the IBM-PC (and others), many, many years ago.  At any rate, the 16550 has a lot of communication features and some very-specific physical attributes, like fixed-size data buffers, hardware handshake management, parity bit management, baud-rate range/control, etc.  However most simple devices with serial interfaces these days only need a couple of basic speeds and XON/XOFF software handshaking.  Consequently most-all of the no-name generic USB-Serial adapters/drivers out there only support some of the basic 16550 functions.  This means they work with simple serial devices but maybe not more-sophisticated serial devices and programs that need and expect more of the features and functions of the 16550.  Most of the 16550 emulation is done in the driver code and not in the actual converter's electronics.  This means that SOMETIMES, a driver update can solve certain communications problems.
* Black-market clones of popular chips and other electronic components.  This has caused a lot of problems for a lot of electronics manufacturers.  Prolific has been hit-hard by a rash of counterfeit chips with their name stamped on top.  A few years back, Panasonic and Toshiba both had major incidents with exploding laptops caused by poor-quality LiIon batteries that somehow managed to sneak into their supply chains.  HP had a rash of desktop computer failures caused by counterfeit capacitors and resistors that came from a reputable electronics wholesaler.  So far this has not happened to FTDI and they have taken a number of steps to make sure that each of their chips is certified and can be traced directly back to their factory.
I hope this helps.
Christopher Erickson
Consulting Engineer
Summit Kinetics
Waikoloa, HI 96738

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