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

8.2.11. Hardware Auto Flow-Control

Hardware based auto flow-control uses 2 signals (cts_n & rts_n) from the Modem Control/Status group. With Hardware auto flow-control disabled, these signals will directly drive the Modem Status register (cts_n) or be driven by the Modem Control register (rts_n).

With auto flow-control enabled, these signals perform flow-control duty with another UART at the other end.

The cts_n input is, when active (low state), will allow the Tx FIFO to send data to the transmit buffer. When cts_n is inactive (high state), the Tx FIFO stops sending data to the transmit buffer. cts_n is expected to be connected to the rts_n output of the other UART.

The rts_n output will go active (low state), when the Rx FIFO is empty, signaling to the opposite UART that it is ready for data. The rts_n output goes inactive (high state) when the Rx FIFO level is reached, signaling to the opposite UART that the FIFO is about to go full and it should stop transmitting.

Due to the delays within the UART logic, one additional character may be transmitted after cts_n is sampled active low. For the same reason, the Rx FIFO will accommodate up to 1 additional character after asserting rts_n (this is allowed because Rx FIFO trigger level is at worst, two entries from being truly full). Both are observed to prevent overflow/underflow between UARTs.

Figure 34. Hardware Auto Flow-Control Between two UARTs