Embedded Peripherals IP User Guide

ID 683130
Date 10/24/2025
Public
Document Table of Contents
1. Introduction 2. Avalon® -ST Serial Peripheral Interface Core 3. SPI Core 4. SPI Agent/JTAG to Avalon® Host Bridge Cores 5. Intel eSPI Agent Core 6. eSPI to LPC Bridge Core 7. Ethernet MDIO Core 8. Intel FPGA 16550 Compatible UART Core 9. UART Core 10. Lightweight UART Core 11. JTAG UART Core 12. Intel FPGA Avalon® Mailbox Core 13. Intel FPGA Avalon® Mutex Core 14. Intel FPGA Avalon® I2C (Host) Core 15. Intel FPGA I2C Agent to Avalon® -MM Host Bridge Core 16. EPCS/EPCQA Serial Flash Controller Core 17. Intel FPGA Serial Flash Controller Core 18. Intel FPGA Serial Flash Controller II Core 19. Intel FPGA Generic QUAD SPI Controller Core 20. Intel FPGA Generic QUAD SPI Controller II Core 21. Interval Timer Core 22. Intel FPGA Avalon FIFO Memory Core 23. On-Chip Memory (RAM and ROM) Intel FPGA IP 24. On-Chip Memory II (RAM or ROM) Intel FPGA IP 25. PIO Core 26. PLL Cores 27. DMA Controller Core 28. Modular Scatter-Gather DMA Core 29. Scatter-Gather DMA Controller Core 30. Video Sync Generator and Pixel Converter Cores 31. Intel FPGA Interrupt Latency Counter Core 32. Performance Counter Unit Core 33. Vectored Interrupt Controller Core 34. System ID Peripheral Core 35. Intel FPGA GMII to RGMII Converter Core 36. HPS GMII to RGMII Adapter IP 37. Intel FPGA MII to RMII Converter Core 38. HPS GMII to TSE 1000BASE-X/SGMII PCS Bridge Core IP 39. Intel FPGA HPS EMAC to Multi-rate PHY GMII Adapter Core 40. Intel FPGA MSI to GIC Generator Core 41. Cache Coherency Translator IP 42. Altera ACE5-Lite Cache Coherency Translator

10.2.4. Handshaking Signal (CTS/RTS Flow Control)

Lightweight UART Core support full-duplex data transmission. If parameter Include CTS/RTS is enabled, the Lightweight UART Core will include handshaking signal which are rts_n (request to send) and cts_n (clear to send). Output of rts_n signal is used to indicate if the core is ready to accept new data and read cts_n to check if the core is allowed to send data to the other device.

When Lightweight UART core acts as a transmitter, you should assert rts_n by writing to RTS bit of control register at address offset 0x3 to request for data transmission. You should monitor the cts_n signal by reading CTS bit of status register at address offset 0x2 to check if the core is allowed to send data to the other device. Data transmission will take place when the Lightweight UART Core receives asserted cts_n signal. Txdata that have been written into TXFIFO will be shifted out via TXD stream.

As described in the following figure, if data transmission has been stopped by cts_n signal deasserted by the other device, the transmit shift register will stop loading the next txdata from the TXFIFO until cts_n is asserted again. Note that the core will still continue to shift out the remaining bits of the txdata that has been loaded in transmit shift register via TXD stream until the transmit shift register is empty. You can de-assert rts_n when transmit data empty bit of status register is HIGH to indicate the completion of data transfer.

Figure 38. Flow Control in Lightweight UART Transmitter

When the Lightweight UART core acts as a receiver, before asserting rts_n, you should read the RXFIFO almost full bit of status register at address offset 0x2 to check if the Lightweight UART core is ready to accept new data from RXD stream.

As described in the following figure, during data transmission, when RXFIFO hits almost full, the Lightweight UART Core will de-assert rts_n automatically to halt data transmission to indicate that the core is not ready to accept new data. You should read out rxdata from RXFIFO in order to resume data transmission process. When the core detect RXFIFO is not almost full, the IP will re-assert back rts_n automatically to accept new data. The remaining RXFIFO depth to assert almost full status can be configurable in GUI.

Figure 39. Flow Control in Lightweight UART Receiver
Note: When the Include CTS/RTS parameter is not enabled, the Lightweight UART transmitter will shift out all the txdata in TXFIFO and transmit shift register continuously until it is empty. Moreover, the Lightweight UART receiver may experience data loss due RXFIFO overflow because it is unable to halt data transmission when RXFIFO is full.