CS5535 datasheet(371/555 Pages) NSC

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UART/IR Controller Register Descriptions (Continued)

EIR, Non-Extended Mode (EXCR1.EXT_SL = 0)

In non-extended UART mode, the functional block prioritizes interrupts into four levels. The EIR indicates the highest level

of interrupt that is pending. See Table 5-33 for the encoding of these interrupts.

EIR Non-Extended Mode Register Map

FEN1

FEN0

RSVD

RXFT

IPR1

IPR0

IPF

EIR Non-Extended Mode Bit Descriptions

Bit

Name

Description

7:6

FEN[1:0]

FIFOs Enabled.

00: No FIFO enabled (Default).

11: FIFOs enabled (bit 0 of FCR = 1).

01, 10: Reserved.

5:4

RSVD

Reserved. Write to 0.

3RXFT

RX_FIFO Timeout. In the 16450 mode, this bit is always 0. In the 16550 mode (FIFOs

enabled), this bit is set to 1 when an RX_FIFO read timeout has occurred and the associ-

ated interrupt is currently the highest priority pending interrupt.

2:1

IPR[1:0]

Interrupt Priority. When bit 0 (IPF) is 0, these bits indicate the pending interrupt with the

highest priority. (Default = 00). See Table 5-33.

0IPF

Interrupt Pending Flag.

0: Interrupt pending.

1: No interrupt pending (Default).

Table 5-33. EIR Non-Extended Mode Interrupt Priorities

EIR

Bits[3:0]

Priority

Level

Interrupt Type

Interrupt Source

Interrupt Reset Control

0001

N/A

None

N/A

0110

Highest

Link Status

Parity error, framing error, data over-

run or break event.

Read Link Status Register (LSR).

0100

Second

Receiver High

Data Level Event

Receiver Holding Register (RXD) is

full, or RX_FIFO level is equal to or

above the threshold.

Reading the RXD or RX_FIFO

level drops below threshold.

1100

Second

RX_FIFO Timeout

At least one character is in the

RX_FIFO, and no character has

been input to or read from the

RX_FIFO for four character times.

Reading the RXD port.

0010

Third

Transmitter Low

Data Level Event

Transmitter Holding Register or

TX_FIFO empty.

Reading the Event Identification

currently the highest priority

pending interrupt, or writing into

the TXD port.

0000

Fourth

Modem Status

Any transition on CTS, DSR or DCD

or a high-to-low transition on RI.

Reading the Modem Status Reg-

ister (MSR).

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