MSC8144E Reference Manual, Rev. 3
20-10
Freescale
Semiconductor
UART
20.1.3 Idle Characters
An idle character contains all logic 1s and has no start, stop, or parity bit. The length of idle
characters depends on the M bit in SCICR. The preamble is a synchronizing idle character that
begins the first transmission initiated after the SCICR[TE] bit is written from 0 to 1. Clearing and
then setting the SCICR[TE] bit during a transmission queues an idle character to be sent after the
frame currently being transmitted.
Note:
When queuing an idle character, return the SCICR[TE] bit to logic 1 before the stop bit
of the current frame shifts out to
UTXD
. Setting SCICR[TE] after the stop bit appears on
UTXD
discards data previously written to the SCI data register. Toggle the SCICR[TE]
bit for a queued idle character while the TDRE flag is set and immediately before
writing the next character to the SCI data register. See Figure 20-7, Queuing an Idle
Character.
20.1.4 Parity Bit Generation
The UART can be configured to enable parity bit generation by the parity enable bit
(SCICR[PE]). The parity type bit (SCICR[PT]) determines whether to place even or odd parity at
T8 (if M = 1) or at T7 (if M = 0) bits of SCIDR.
20.2 Receiver
The SCI receiver can accommodate either 8-bit or 9-bit data characters. The state of the
SCICR[M] bit determines the length of data characters. When receiving 9-bit data, bit R8 in the
SCIDR is the ninth bit (bit 8).
Figure 20-7. Queuing an Idle Character
Start
Bit
Stop
Bit
Start
Bit
Stop
Bit
Character
Next Data
Character
Idle
UTXD
Stop
Bit
TDRE flag
is set
Toggle
TE bit
Write next
data character
to SCIDR
Character
Current Data
Содержание MSC8144E
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