UM10413
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 1 — 16 December 2011
84 of 268
NXP Semiconductors
UM10413
MPT612 User manual
Interrupts are handled as described in
. Given the status of U0IIR[3:0], an
interrupt handler routine can determine the cause of the interrupt and how to clear the
active interrupt. In order to clear the interrupt before exiting the Interrupt Service Routine,
the U0IIR must be read.
The UART0 RLS interrupt (U0IIR[3:1] = 011) is the highest priority interrupt and is set
whenever any one of four error conditions occur on the UART0 Rx input: Overrun Error
(OE), Parity Error (PE), Framing Error (FE) and Break Interrupt (BI). The UART0 Rx error
condition that sets the interrupt can be observed via U0LSR[4:1]. The interrupt is cleared
after an U0LSR read.
The UART0 RDA interrupt (U0IIR[3:1] = 010) shares the second-level priority with the CTI
interrupt (U0IIR[3:1] = 110). The RDA is activated when the UART0 Rx FIFO reaches the
trigger level defined in U0FCR[7:6] and is reset when the UART0 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.
The CTI interrupt (U0IIR[3:1] = 110) is a second-level interrupt and is set when the UART0
Rx FIFO contains at least one character and no UART0 Rx FIFO activity has occurred in
3.5 to 4.5 character times. Any UART0 Rx FIFO activity (read or write of UART0 RSR)
clears the interrupt. This interrupt is intended to flush the UART0 RBR after a message is
received that is not a multiple of the trigger level size. For example, if a peripheral wished
to send a 105 character message and the trigger level was 10 characters, the CPU would
receive 10 RDA interrupts resulting in the transfer of 100 characters and 1 to 5 CTI
interrupts (depending on the service routine) resulting in the transfer of the remaining 5
characters.
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 must not write logic 1s to reserved
bits; value read from a reserved bit is not defined
n/a
Table 90:
UART0 Interrupt identification register (UOIIR - address 0xE000 C008, read only)
bit description
…continued
Bit
Symbol
Value Description
Reset
value
Table 91:
UART0 interrupt handling
U0IIR[3:0]
value
Priority
Interrupt type
Interrupt source
Interrupt reset
0001
-
none
none
-
0110
highest
Rx line status/error
OE
U0LSR read