Serial Communications Interface (SCI)
Functional Description
MC68HC908AZ60A — Rev 2.0 Technical Data
MOTOROLA Serial Communications Interface (SCI) 253
consist of a valid start bit, eight or nine data bits (as defined by the M bit
in SCC1) of logic 0 and one half data bit length of logic 0 in the stop bit
position followed immediately by the idle character. To ensure a break
character of the proper length is transmitted, always queue up a byte of
data to be transmitted while the final break sequence is in progress.
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 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.
18.5.2.5 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 1.
(See SCI Control Register 1.)
18.5.2.6 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.
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.
