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

10.2.6. Receiver Logic

The Lightweight UART receiver consists of a 7-, 8-, or 9-bit receiver-shift register and a corresponding 7-, 8-, or 9-bit width of RXFIFO. The RXFIFO can be implemented either in register with configurable depth or a fixed depth that is able to fully utilize a single memory block.

Avalon® memory-mapped host peripherals read the RXFIFO via the Avalon® memory-mapped agent port. The RXFIFO is loaded from the receiver shift register automatically every time a new character is fully received.

These two registers provide double buffering. The RXFIFO can hold previously received character while the subsequent character from RXD stream is being shifted into the receiver shift register.

A host peripheral can monitor the receiver's status by reading the status register's receive character ready (RRDY), RXFIFO overrun error (ROE), RXFIFO underrun error (RUE), RXFIFO full (RFULL), RXFIFO almost full (RAFULL), break detect (BRK), parity error (PE), and framing error (FE) bits. The remaining RXFIFO depth to assert almost full status can be configurable in GUI. The receiver logic checks for five exceptional conditions, which are framing error, parity error, RXFIFO overrun error, RXFIFO underrun error and break detect, in the received data and sets corresponding status register bits. If the RXFIFO overrun error, RXFIFO underrun error, break detect, parity error, or framing error occurs, the corresponding status bit is set and remains HIGH until it is cleared by writing to the status register.

You can only read the data from RXFIFO when the RRDY bits is HIGH, which indicates that RXFIFO is not empty. You will encounter RXFIFO underrun error if you read the data from RXFIFO when the RRDY bits is LOW. When the underrun error occurs, the additional read transaction when RXFIFO is empty will give a default value, which is 0x000F. When RXFIFO is full, the next received character from RXD stream will not be able to fill in RXFIFO and the data will be missing, causing overrun error. The existing data that is stored in RXFIFO will not be overwritten.

You can monitor the RXFIFO filled level by reading the value of RXFIFO_LVL register. Note that when RXFIFO is full, rxfifo level will roll over to 0. Thus, the value 0 of RXFIFO_LVL could either represent RXFIFO is empty only when the status register's receive character ready (RRDY) bit is LOW, otherwise, it means that RXFIFO is full.

The receiver logic automatically detects the correct number of start, stop, and parity bits in the serial RXD stream as required by the RS-232 specification.