MC68HC08AS32 Datasheet, PDF (245/394 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

Serial Communications Interface (SCI)
Functional Description
17.4.6 Idle Characters
An idle character contains all logic 1s and has no start, stop, or parity bit.
Idle character length depends on the M bit (mode character length) in
SCC1. The preamble is a synchronizing idle character that begins every
transmission.
If the TE bit (transmitter enable) is cleared during a transmission, the
PTE0/TxD pin becomes idle after completion of the transmission in
progress. Clearing and then setting the TE bit during a transmission
queues an idle character to be sent after the character currently being
transmitted.
NOTE:
When queueing an idle character, return the TE bit to logic 1 before the
stop bit of the current character shifts out to the PTE0/TxD pin. Setting
TE after the stop bit appears on PTE0/TxD causes loss of data
previously written to the SCDR.
A good time to toggle the TE bit is when the SCTE bit becomes set and
just before writing the next byte to the SCDR.
17.4.7 Inversion of Transmitted Output
The transmit inversion bit (TXINV) in SCI control register 1 (SCC1)
reverses the polarity of transmitted data. All transmitted values, including
idle, break, start, and stop bits, are inverted when TXINV is at logic 1.
(See 17.9.1 SCI Control Register 1.)
MC68HC08AS32 — Rev. 3.0
MOTOROLA
Serial Communications Interface (SCI)
Advance Information
245