Visible to Intel only — GUID: iga1405469069814
Ixiasoft
Visible to Intel only — GUID: iga1405469069814
Ixiasoft
11.4.3.3. status Register
The status register consists of individual bits that indicate particular conditions inside the UART core. Each status bit is associated with a corresponding interrupt-enable bit in the control register. The status register can be read at any time. Reading does not change the value of any of the bits. Writing zero to the status register clears the DCTS, E, TOE, ROE, BRK, FE, and PE bits.
Bit | Name | Access | Description |
---|---|---|---|
0 18 | PE | RC | Parity error. A parity error occurs when the received parity bit has an unexpected (incorrect) logic level. The PE bit is set to 1 when the core receives a character with an incorrect parity bit. The PE bit stays set to 1 until it is explicitly cleared by a write to the status register. When the PE bit is set, reading from the rxdata register produces an undefined value. If the Parity hardware option is not enabled, no parity checking is performed and the PE bit always reads 0. Refer to Data Bits, Stop Bits, Parity section. |
1 | FE | RC | Framing error. A framing error occurs when the receiver fails to detect a correct stop bit. The FE bit is set to 1 when the core receives a character with an incorrect stop bit. The FE bit stays set to 1 until it is explicitly cleared by a write to the status register. When the FE bit is set, reading from the rxdata register produces an undefined value. |
2 | BRK | RC | Break detect. The receiver logic detects a break when the RXD pin is held low (logic 0) continuously for longer than a full-character time (data bits, plus start, stop, and parity bits). When a break is detected, the BRK bit is set to 1. The BRK bit stays set to 1 until it is explicitly cleared by a write to the status register. |
3 | ROE | RC | Receive overrun error. A receive-overrun error occurs when a newly received character is transferred into the rxdata holding register before the previous character is read (in other words, while the RRDY bit is 1). In this case, the ROE bit is set to 1, and the previous contents of rxdata are overwritten with the new character. The ROE bit stays set to 1 until it is explicitly cleared by a write to the status register. |
4 | TOE | RC | Transmit overrun error. A transmit-overrun error occurs when a new character is written to the txdata holding register before the previous character is transferred into the shift register (in other words, while the TRDY bit is 0). In this case the TOE bit is set to 1. The TOE bit stays set to 1 until it is explicitly cleared by a write to the status register. |
5 | TMT | R | Transmit empty. The TMT bit indicates the transmitter shift register’s current state. When the shift register is in the process of shifting a character out the TXD pin, TMT is set to 0. When the shift register is idle (in other words, a character is not being transmitted) the TMT bit is 1. An Avalon® -MM host peripheral can determine if a transmission is completed (and received at the other end of a serial link) by checking the TMT bit. |
6 | TRDY | R | Transmit ready. The TRDY bit indicates the txdata holding register’s current state. When the txdata register is empty, it is ready for a new character, and TRDY is 1. When the txdata register is full, TRDY is 0. An Avalon® -MM host peripheral must wait for TRDY to be 1 before writing new data to txdata. |
7 | RRDY | R | Receive character ready. The RRDY bit indicates the rxdata holding register’s current state. When the rxdata register is empty, it is not ready to be read and RRDY is 0. When a newly received value is transferred into the rxdata register, RRDY is set to 1. Reading the rxdata register clears the RRDY bit to 0. An Avalon® -MM host peripheral must wait for RRDY to equal 1 before reading the rxdata register. |
8 | E | RC | Exception. The E bit indicates that an exception condition occurred. The E bit is a logical-OR of the TOE, ROE, BRK, FE, and PE bits. The E bit and its corresponding interrupt-enable bit (IE) bit in the control register provide a convenient method to enable/disable IRQs for all error conditions. The E bit is set to 0 by a write operation to the status register. |
10 18 | DCTS | RC | Change in clear to send (CTS) signal. The DCTS bit is set to 1 whenever a logic-level transition is detected on the CTS_N input port (sampled synchronously to the Avalon® -MM clock). This bit is set by both falling and rising transitions on CTS_N. The DCTS bit stays set to 1 until it is explicitly cleared by a write to the status register. |
11 18 | CTS | R | Clear-to-send (CTS) signal. The CTS bit reflects the CTS_N input’s instantaneous state (sampled synchronously to the Avalon® -MM clock). The CTS_N input has no effect on the transmit or receive processes. The only visible effect of the CTS_N input is the state of the CTS and DCTS bits, and an IRQ that can be generated when the control register’s idcts bit is enabled. |
12 18 | EOP | R18 | End of packet encountered. The EOP bit is set to 1 by one of the following events: An EOP character is written to txdata An EOP character is read from rxdata The EOP character is determined by the contents of the endofpacket register. The EOP bit stays set to 1 until it is explicitly cleared by a write to the status register. If the Include End-of-Packet Register hardware option is not enabled, the EOP bit always reads 0. Refer to Streaming Data (DMA) Control Section. |