UART with FIFOs and Synchronous CPU Interface Core

Cast LogoThe H16550S is a standard UART providing 100% software compatibility with the popular Texas Instruments 16550 device. It performs serial-to-parallel conversion on data originating from modems or other serial devices, and performs parallel-to-serial conversion on data from a CPU to these devices.

The H16550S can be run in either 16450-compatible character mode or in 16550-compatible FIFO mode, where an internal FIFO relieves the CPU of excessive software overhead.

Developed for easy reuse, the H16550S is available optimized for several Lattice devices, with competitive utilization and performance characteristics.


  • Capable of running all existing 16450 and 16550a software
  • Fully Synchronous design. All inputs and outputs are based on rising edge of clock
  • In FIFO mode, the transmitter and receiver are each buffered with 16 byte FIFOs to reduce the number of interrupts presented to the CPU
  • Adds or deletes standard asynchronous communication bits (start, stop and parity) to or from the serial data
  • Independently controlled transmit, receive, line status and data set interrupts
  • Programmable baud generator divides any input clock by 1 to (216 - 1) and generates the 16 x clock
  • Modem control functions (CTSn, RTSn, DSRn, DTRn, RIn, and DCDn)
  • Fully programmable serial interface characteristics:
    • 5, 6, 7, or 8 bit characters
    • Even, odd, or no-parity bit generation and detection
    • 1, 1_, or 2 stop bit generation
    • Baud generation
  • False start bit detection
  • Complete status register
  • Internal diagnostic capabilities: loopback controls for communications link fault isolation
  • Full prioritized interrupt system controls


  • Serial or modem computer interface
  • Serial interface within modems and other devices

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Block Diagram

Performance and Size

The following are typical performance and utilization results.

Lattice Device Slices PFUs Block RAMs External I/Os Speed (fmax, MHz)
LFE2-50-7 688 451 272 2 39 156
LFXP2-17E-7 587 442 267 2 39 82

Ordering Information

This IP core is supported and sold by CAST, contact CAST at or visit their website at for more information.


Quick Reference
H16550S UART with FIFOs and Synchronous CPU Interface Core Data Sheet
5/3/2016 PDF
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