mc68hc11d0cfn2 Freescale Semiconductor, Inc, mc68hc11d0cfn2 Datasheet - Page 84

• Manufacturer Part Number: mc68hc11d0cfn2
• Description: M68hc11 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Serial Communications Interface (SCI)
Data Sheet
84
TDRE and TC flags are normally set when the transmitter is first enabled (TE set
to 1). The TDRE flag indicates there is room in the transmit queue to store another
data character in the TDR. The TIE bit is the local interrupt mask for TDRE. When
TIE is 0, TDRE must be polled. When TIE and TDRE are 1, an interrupt is
requested.
The TC flag indicates the transmitter has completed the queue. The TCIE bit is the
local interrupt mask for TC. When TCIE is 0, TC must be polled; when TCIE is 1
and TC is 1, an interrupt is requested.
Writing a 0 to TE requests that the transmitter stop when it can. The transmitter
completes any transmission in progress before actually shutting down. Only an
MCU reset can cause the transmitter to stop and shut down immediately. If TE is
written to 0 when the transmitter is already idle, the pin reverts to its
general-purpose I/O function (synchronized to the bit-rate clock). If anything is
being transmitted when TE is written to 0, that character is completed before the
pin reverts to general-purpose I/O, but any other characters waiting in the transmit
queue are lost. The TC and TDRE flags are set at the completion of this last
character, even though TE has been disabled.
The SCI receiver has five status flags, three of which can generate interrupt
requests. The status flags are set by the SCI logic in response to specific conditions
in the receiver. These flags can be read (polled) at any time by software. Refer to
Figure
When an overrun takes place, the new character is lost, and the character that was
in its way in the parallel RDR is undisturbed. RDRF is set when a character has
been received and transferred into the parallel RDR. The OR flag is set instead of
RDRF if overrun occurs. A new character is ready to be transferred into RDR
before a previous character is read from RDR.
The NF and FE flags provide additional information about the character in the RDR,
but do not generate interrupt requests.
The last receiver status flag and interrupt source come from the IDLE flag. The RxD
line is idle if it has constantly been at logic 1 for a full character time. The IDLE flag
is set only after the RxD line has been busy and becomes idle, which prevents
repeated interrupts for the whole time RxD remains idle.
Freescale Semiconductor, Inc.
6-9, which shows SCI interrupt arbitration.
For More Information On This Product,
Serial Communications Interface (SCI)
Go to: www.freescale.com
MC68HC711D3 — Rev. 2
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