What does 450, 550, 750 UART compatibility mean, and why is there no 950 ?


Over time new models of UART have been designed, some specifications have become industry standards (such as 450, 550 and 750) others either were superseded too quickly or no definitive spec was universally accepted.

Today there is no industry standard for a 950 UART, there are minor differences between the current chip manufacturers (including Brainboxes) who all produce 950 labelled devices.

Brainboxes 16PCI958 contains eight independent 950 UART product which has been designed in house from the ground up specifically to produce the best in class PCI cards using the lowest Bill Of Material count parts. Thus this chip has a fully validated PCI interface integrated with one to eight UARTs, there are internal pull ups on all inputs negating the need to place discrete pull up resistors on the pcb, there is auto-gating circuitry for when a port is used in RS485 two wire mode. The chip can also be configured as one to four 950 UARTS with an industry standard LPT port.

  • The 750 standard is compatibility with Texas instruments 16C750 UART
  • The 550 standard is compatibility with National Semiconductors 16C550 UART
  • The 450 standard is compatibility with National Semiconductors 16C450 UART
  • The original UART used in the IBM PC was  the Intel 8250 UART

When Brainboxes brainboxes products list compatibility they are ultimately showing they are compatibility with the models in this list.

No one was able to establish a 650 UART as an industry standard though several companies released one 650 badged UARTS- probably because Texas trumped the 650s with a better designed product whose functionality, pricing and marketing was so good that the TI 750 became a widely accepted standard in the PC industry.

No one was able to establish an 850 UART as an industry standard though again several have been released.

More information about UARTs

RS232/422/485 Adaptors >>