Serial Communications Interface (SCI) Module
Data Sheet
MC68HC08GP32A MC68HC08GP16A
156
Serial Communications Interface (SCI) Module
MOTOROLA
14.4.2.4 Idle Characters
An idle character contains all 1s and has no start, stop, or parity bit. Idle character
length depends on the M bit in SCC1. The preamble is a synchronizing idle
character that begins every transmission.
If the TE bit 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 1 before the stop bit of the
current character shifts out to the TxD pin. Setting TE after the stop bit appears on
TxD causes data previously written to the SCDR to be lost.
Toggle the TE bit for a queued idle character when the SCTE bit becomes set and
just before writing the next byte to the SCDR.
14.4.2.5 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,
14.4.2.6 Transmitter Interrupts
These conditions can generate CPU interrupt requests from the SCI transmitter:
SCI transmitter empty (SCTE) — The SCTE bit in SCS1 indicates that the
SCDR has transferred a character to the transmit shift register. SCTE can
generate a transmitter CPU interrupt request. Setting the SCI transmit
interrupt enable bit, SCTIE, in SCC2 enables the SCTE bit to generate
transmitter CPU interrupt requests.
Transmission complete (TC) — The TC bit in SCS1 indicates that the
transmit shift register and the SCDR are empty and that no break or idle
character has been generated. The transmission complete interrupt enable
bit, TCIE, in SCC2 enables the TC bit to generate transmitter CPU interrupt
requests.
14.4.3 Receiver
14.4.3.1 Character Length
The receiver can accommodate either 8-bit or 9-bit data. The state of the M bit in
SCI control register 1 (SCC1) determines character length. When receiving 9-bit
data, bit R8 in SCI control register 2 (SCC2) is the ninth bit (bit 8). When receiving
8-bit data, bit R8 is a copy of the eighth bit (bit 7).