Feeling nostalgic about COM ports? So are we and our motherboards. This article will be a brief overview of what to expect when adding COM ports to a modern computer. First, we need to define “COM port” because even Google thinks COM ports are irrelevant. Communication port or COM port is the asynchronous serial data transfer between devices.
USB is the standard serial communication protocol, forsaking all others. So why add COM ports to your system? There is an existing population of legacy systems that still require COM ports. Sensors, PLCs, and other controllers.
*Links to vendors and pricing is for information purposes only and not an endorsement of the product. Do your research to find the best product and price for you.
TTL (Transistor-transistor Logic) – typically a single transmission line accompanied by a ground wire. 0V to 0.8V is low/ “0”, 2V to 5V is high/ “1”.
UART (Universal asynchronous receiver-transmitter) $ – TX and RX usually TTL voltage levels
RS232 $ – Similar to UART but with voltage levels between -25V and +25V. Extra signal flag wires. Only 1 commanding and 1 listening device.
RS422 $$ – Similar to RS232 but with differential TX and RX lines. Extra single flags. Only 1 commanding device and multiple listening devices.
RS485 $$ – Similar to RS422 but with multiple commanding and multiple listening devices.
MIL-STD-1553 $$$$ – Multiple channels and redundancy
USB $ – Gold standard in serial communication
Quantum Entanglement $$$$$
Waveless Communication $$$$$
The most common and inexpensive ways to add COM ports is use PCI-E or USB components.
Most motherboards do NOT have a native COM port and straight connection bracket will not work. If the motherboard DOES have a native COM port, 99% of the time it is only UART/RS232. The COM port does not have differential pins to support RS422/RS485 so don’t expect native RS422 on a motherboard.
A PCIE card is your best bet for building in COM ports to a system. The card can work in any PCIE slot as it only takes 1 lane for a dual COM port card.
USB to Serial cables
A USB to Serial cable is a great solution if the device needs to move between systems. The downside is having to install a driver everyone time on new systems.
1553 PCI and PCIE cards are typically used for military and avionic vehicles. The cards have various options and not something you will find on Amazon or an electronics store. USB versions are also available for a similar price.