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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
276 of 571
NXP Semiconductors
UM10316
Chapter 19: LPC29xx Universal Asynchronous Receiver/Transmitter
Bit UnIIR[9:8] are set by the auto-baud function and signal a time-out or end of auto-baud
condition. The auto-baud interrupt conditions are cleared by setting the corresponding
Clear bits in the Auto-baud Control Register.
If the IntStatus bit is 1 no interrupt is pending and the IntId bits will be zero. If the IntStatus
is 0, a non auto-baud interrupt is pending in which case the IntId bits identify the type of
interrupt and handling as described in
. Given the status of UnIIR[3:0], an
interrupt handler routine can determine the cause of the interrupt and how to clear the
active interrupt. The UnIIR must be read in order to clear the interrupt prior to exiting the
Interrupt Service Routine.
The UARTn RLS interrupt (UnIIR[3:1] = 011) is the highest priority interrupt and is set
whenever any one of four error conditions occur on the UARTn Rx input: overrun error
(OE), parity error (PE), framing error (FE) and break interrupt (BI). The UARTn Rx error
condition that set the interrupt can be observed via U0LSR[4:1]. The interrupt is cleared
upon an UnLSR read.
The UARTn RDA interrupt (UnIIR[3:1] = 010) shares the second level priority with the CTI
interrupt (UnIIR[3:1] = 110). The RDA is activated when the UARTn Rx FIFO reaches the
trigger level defined in UnFCR[7:6] and is reset when the UARTn Rx FIFO depth falls
below the trigger level. When the RDA interrupt goes active, the CPU can read a block of
data defined by the trigger level.
Table 234. UARTn Interrupt Identification Register (U0IIR - address 0xE004 5008,
U1IIR - 0xE004 6008, Read Only) bit description
Bit
Symbol
Value
Description
Reset
Value
0
IntStatus
0
Interrupt status. Note that U1IIR[0] is active low. The
pending interrupt can be determined by evaluating
UnIIR[3:1].
1
At least one interrupt is pending.
1
No interrupt is pending.
3:1
IntId
011
Interrupt identification. UnIER[3:1] identifies an interrupt
corresponding to the UARTn Rx FIFO. All other
combinations of UnIER[3:1] not listed above are reserved
(000,100,101,111).
0
1 - Receive Line Status (RLS).
010
2a - Receive Data Available (RDA).
110
2b - Character Time-out Indicator (CTI).
001
3 - THRE Interrupt
5:4
-
Reserved, user software should not write ones to reserved
bits. The value read from a reserved bit is not defined.
NA
7:6
FIFO Enable
These bits are equivalent to UnFCR[0].
0
8
ABEOInt
End of auto-baud interrupt. True if auto-baud has finished
successfully and interrupt is enabled.
0
9
ABTOInt
Auto-baud time-out interrupt. True if auto-baud has timed
out and interrupt is enabled.
0
31:10 -
Reserved, user software should not write ones to reserved
bits. The value read from a reserved bit is not defined.
NA