MC68HC11KW1 Datasheet, PDF(141/238 Page) Motorola, Inc – High-density complementary metal oxide semiconductor HCMOS) microcontroller unit

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MC68HC11KW1 Datasheet, PDF (141/238 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor HCMOS) microcontroller unit

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The TC ï¬ag indicates the transmitter has completed the queue. The TCIE bit is the local interrupt

mask for TC. When TCIE is zero, TC must be polled; when TCIE is one and TC is one, an interrupt

is requested.

Writing a zero to TE requests that the transmitter stop when it can. The transmitter completes any

transmission in progress before shutting down. Only an MCU reset can cause the transmitter to

stop and shut down immediately. If TE is cleared 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 cleared, 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

ï¬ags are set at the completion of this last character, even though TE has been disabled.

7.7.1 Receiver ï¬ags

The SCI receiver has seven status ï¬ags, three of which can generate interrupt requests. The

status ï¬ags are set by the SCI logic in response to speciï¬c conditions in the receiver. These ï¬ags

can be read (polled) at any time by software. Refer to Figure 7-3, which shows SCI interrupt

arbitration.

When an overrun takes place, the new character is lost, and the character that was in its way in

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the parallel receive data register (RDR) is undisturbed. RDRF is set when a character has been

received and transferred into the parallel RDR. The OR ï¬ag is set instead of RDRF if overrun

occurs. A new character is ready to be transferred into the RDR before a previous character is read

from the RDR.

The NF, FE and PF ï¬ags provide additional information about the character in the RDR, but do not

generate interrupt requests.

The receiver active ï¬ag (RAF) indicates that the receiver is busy.

The last receiver status ï¬ag and interrupt source come from the IDLE ï¬ag. The RXD line is idle if it has

constantly been at logic one for a full character time. The IDLE ï¬ag is set only after the RXD line has

been busy and becomes idle. This prevents repeated interrupts for the time RXD remains idle.

MC68HC11KW1

SERIAL COMMUNICATIONS INTERFACE

7-13

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