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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—Universal Asynchronous
Receiver-Transmitter (UART)
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
758
Order Number: 306262-004US
In FIFO mode, each received character carries the line status along with the character.
When in FIFO Mode, the Receive Line Status Interrupt will be active on the character
located in the bottom of the Receive FIFO. If a Line Status error condition is detected
on the character in the bottom of the Receive FIFO, a Receive Line Status Interrupt is
generated. Reading the Line Status Register clears the Receive Line Status Interrupt.
When in Non-FIFO Mode, the Receive Line Status Interrupt will be active on the
character located in the bottom of the Receive Buffer Register. If a line-status error
condition is detected on the character in the Receive Buffer Register, a Receive Line
Status Interrupt is generated.
The Receiver Data Available Interrupt Enable allows interrupts to be generated to the
Interrupt Controller for the IXP45X/IXP46X network processors and captured in the
UART Interrupt Identification Register (IIR) when UART data is available to be read by
the Intel XScale processor.
When the UART is in FIFO mode, the Receive Data Available interrupt will be encoded in
the Interrupt Identification Register, after the FIFO trigger level defined in the FIFO
Control Register (FCR) is reached. When the UART is in non-FIFO mode, the Receive
Data Available interrupt will be encoded in the Interrupt Identification Register after
data is in the Receive Buffer Register (RBR).
When operating in FIFO Mode, the Receive Data Available Interrupt is cleared, when
the FIFO drops below the programmed trigger level. When operating in Non-FIFO
Mode, the Receive Data Available Interrupt is cleared when the received character is
read by the IXP45X/IXP46X network processors from the Receive Holding Register.
The Receiver Interrupt Time Out Enable can be used only in FIFO Mode and allows
interrupts to be generated to the Interrupt Controller for the IXP45X/IXP46X network
processors and captured in the UART Interrupt Identification Register (IIR). This
happens when:
• At least one character is available in the receive FIFO
• The last character received by the UART receive interface occurred more than four
continuous character times ago
• The most-recent read of the receive FIFO by the IXP45X/IXP46X network
processors was more than four continuous character times ago
For example, the maximum time between a received character and a Receive Character
Time-Out Interrupt is 160 ms at 1,200 baud with a 12-bit receive character (i.e., 1
start, 8 data, 1 parity, and 2 stop bits).
The time-out interrupt is cleared by the IXP45X/IXP46X network processors reading the
Receive FIFO or setting the RESETRF bit to logic 1, in the FIFO Control Register.
If a Receive Character Time-Out Interrupt is active, the interrupt-time-out counter will
be reset only after the IXP45X/IXP46X network processors read a character from the
Receive FIFO. If a Receive Character Time-Out Interrupt is non-active, the interrupt
time-out counter will be reset after the IXP45X/IXP46X network processors read a
character from the Receive FIFO or when a new character is placed into the Receive
FIFO by the receive interface.
The Transmit Data Request Interrupt Enable can be used in Non-FIFO mode or FIFO
Mode.
(1/ ((1200characters/second)/12characters))) * 4
characters =
= 0.040 seconds
= 40 ms