
MOTOROLA
9-10
ASYNCHRONOUS SERIAL COMMUNICATIONS INTERFACE
M68HC11
REFERENCE MANUAL
Mark and space parity are trivial, but odd and even parity require software calcula-
tions.
WAKE — Wake-Up Method Select
0 = Idle line; detection of at least a full character time of idle line causes the receiver
to wake up.
1 = Address mark; a logic one in the MSB position (eighth or ninth data bit depend-
ing on character size selected by M bit) causes the receiver to wake up.
9.2.4 SCI Control Register 2 (SCCR2)
The SCCR2 is the main control register for the SCI subsystem.
TIE — Transmit Interrupt Enable
0 = TDRE interrupts disabled (software polling mode).
1 = An SCI interrupt is requested when TDRE is set to one.
TCIE — Transmit Complete Interrupt Enable
0 = TC interrupts disabled (software polling mode).
1 = An SCI interrupt is requested when TC is set to one.
RIE — Receive Interrupt Enable
0 = RDRF and OR interrupts disabled (software polling mode).
1 = An SCI interrupt is requested when either RDRF or OR is set to one.
ILIE — Idle-Line Interrupt Enable
0 = IDLE interrupts disabled (software polling mode).
1 = An SCI interrupt is requested when IDLE is set to one.
The idle-line function is inhibited while the receiver wake-up function is enabled.
TE — Transmit Enable
0 = SCI transmitter disabled
1 = SCI transmitter enabled
The transmitter does not turn off in the middle of a character. When TE is written to
zero, the transmitter keeps control of the TxD pin until any character in progress (in-
cluding preambles or break characters) is finished. When TE is written from zero to
one, the transmitter sends a preamble character consisting of 10 (11 if M = 1) bits of
logic one. This mechanism can be used to queue an idle character time between the
last character of one message and the first character of the succeeding message. The
procedure would be to wait for TDRE to be set after writing the last character to the
SCDR (this signals that the character has transferred to the shifter to be sent serially).
Then write TE to zero and back to one. Since the last character is still being shifted
out, the transmitter will not relinquish control of the TxD pin, but the act of writing TE
from zero to one causes an idle preamble character to be queued to be sent as soon
SCCR2 —
SCI Control Register 2
$102D
BIT 7
TIE
0
6
5
4
3
2
1
BIT 0
SBK
0
TCIE
0
RIE
0
ILIE
0
TE
0
RE
0
RWU
0
RESET: