UM10413
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 1 — 16 December 2011
108 of 268
NXP Semiconductors
UM10413
MPT612 User manual
15.3.11 UART1 Modem status register (U1MSR - 0xE001 0018)
The U1MSR is a read-only register that provides status information on the modem input
signals. U1MSR[3:0] is cleared on U1MSR read.
Remark:
Modem signals have no direct effect on UART1 operation, they facilitate
software implementation of modem signal operations.
2
Parity Error
(PE)
when parity bit of received character is the wrong state, a parity error occurs. An
U1LSR read clears U1LSR[2]. Time of parity error detection is dependent on
U1FCR[0].
Remark:
Parity error is associated with character at top of UART1 RBR FIFO
0
0
parity error status is inactive
1
parity error status is active
3
Framing Error
(FE)
when stop bit of received character is logic 0, a framing error occurs. An U1LSR
read clears U1LSR[3]. Time of framing error detection is dependent on U1FCR0.
On detection of framing error, Rx attempts to resynchronize to data and assumes
that bad stop bit is an early start bit. However, it cannot be assumed that next
received byte is correct even if there is no framing error.
Remark:
Framing error is associated with character at top of UART1 RBR FIFO.
0
0
framing error status is inactive
1
framing error status is active
4
Break Interrupt
(BI)
when RXD1 is held in spacing state (all 0s) for one full character transmission (start,
data, parity, stop), a break interrupt occurs. Once break condition is detected,
receiver is idle until RXD1 enters marking state (all 1s). An U1LSR read clears this
status bit. Time of break detection is dependent on U1FCR[0].
Remark:
Break interrupt is associated with character at top of UART1 RBR FIFO.
0
0
break interrupt status is inactive
1
break interrupt status is active
5
Transmitter
Holding
Register Empty
(THRE)
THRE is set immediately on detection of an empty UART1 THR and is cleared on a
U1THR write
1
0
U1THR contains valid data
1
U1THR is empty
6
Transmitter
Empty
(TEMT)
TEMT is set when both U1THR and U1TSR are empty; TEMT is cleared when
either U1TSR or U1THR contain valid data
1
0
U1THR and/or U1TSR contains valid data
1
U1THR and U1TSR are empty
7
Error in RX
FIFO
(RXFE)
U1LSR[7] is set when a character with a Rx error such as framing error, parity error
or break interrupt, is loaded into U1RBR. Cleared when register U1LSR is read and
there are no subsequent errors in UART1 FIFO.
0
0
U1RBR contains no UART1 Rx errors or U1FCR[0] = 0
1
UART1 RBR contains at least one UART1 Rx error
Table 113. UART1 Line status register (U1LSR - address 0xE001 0014, read only) bit description
…continued
Bit Symbol
Value Description
Reset
value