MEC1404 Datasheet, PDF (288/572 Pages) Microchip Technology – Keyboard and Embedded Controller Products for Notebook PC

MEC140X/1X
17.11.10 LINE STATUS REGISTER
Offset ^05h
Bits
Description
Type
7 FIFO_ERROR
R
This bit is permanently set to logic “0” in the 450 mode. In the
FIFO mode, this bit is set to a logic “1” when there is at least one
parity error, framing error or break indication in the FIFO. This bit
is cleared when the LSR is read if there are no subsequent
errors in the FIFO.
6 TRANSMIT_ERROR
R
Transmitter Empty. Bit 6 is set to a logic “1” whenever the Trans-
mitter Holding Register (THR) and Transmitter Shift Register
(TSR) are both empty. It is reset to logic “0” whenever either the
THR or TSR contains a data character. Bit 6 is a read only bit.
In the FIFO mode this bit is set whenever the THR and TSR are
both empty,
5 TRANSMIT_EMPTY
R
Transmitter Holding Register Empty Bit 5 indicates that the
Serial Port is ready to accept a new character for transmission.
In addition, this bit causes the Serial Port to issue an interrupt
when the Transmitter Holding Register interrupt enable is set
high. The THRE bit is set to a logic “1” when a character is trans-
ferred from the Transmitter Holding Register into the Transmitter
Shift Register. The bit is reset to logic “0” whenever the CPU
loads the Transmitter Holding Register. In the FIFO mode this bit
is set when the XMIT FIFO is empty, it is cleared when at least 1
byte is written to the XMIT FIFO. Bit 5 is a read only bit.
4 BREAK_INTERRUPT
R
Break Interrupt. Bit 4 is set to a logic “1” whenever the received
data input is held in the Spacing state (logic “0”) for longer than a
full word transmission time (that is, the total time of the start bit +
data bits + parity bits + stop bits). The BI is reset after the CPU
reads the contents of the Line Status Register. In the FIFO mode
this error is associated with the particular character in the FIFO it
applies to. This error is indicated when the associated character
is at the top of the FIFO. When break occurs only one zero char-
acter is loaded into the FIFO. Restarting after a break is
received, requires the serial data (RXD) to be logic “1” for at
least 1/2 bit time.
Bits 1 through 4 are the error conditions that produce a Receiver
Line Status Interrupt BIT 3 whenever any of the corresponding
conditions are detected and the interrupt is enabled
Default
0h
Reset
Event
RESET
0h
RESET
0h
RESET
0h
RESET
DS00001956D-page 288
 2015 - 2016 Microchip Technology Inc.