
Serial Communications Interface Module (SCI)
Functional Description
MC68HC(7)08LN56 — Rev. 2.0
General Release Specication
MOTOROLA
Serial Communications Interface Module (SCI)
209
NONDISCLOSURE
AGREEMENT
REQUIRED
If the TE bit is cleared during a transmission, the PTE5/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 one 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.
A good time to toggle the TE bit for a queued idle character is when the
SCTE bit becomes set and just before writing the next byte to the SCDR.
12.5.2.5 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, start, and stop bits, are inverted when TXINV is at logic one.
12.5.2.6 Transmitter Interrupts
The following 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
or a transmitter DMA service request. Setting the SCI transmit
interrupt enable bit, SCTIE, in SCC2 enables the SCTE bit to
generate transmitter CPU interrupt requests. Setting both the
SCTIE bit and the DMA transfer enable bit, DMATE, in SCC3
enables the SCTE bit to generate transmitter DMA service
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.