
Infrared Serial Communications Interface (IrSCI)
MC68HC08LK60 MC68HC908LK60 Advance Information Data Sheet, Rev. 1.1
126
Freescale Semiconductor
12.5.2.3 Break Characters
Writing a logic 1 to the send break bit, SBK, in SCC2 loads the transmit shift register with a break
character. A break character contains all logic 0s and has no start, stop, or parity bit. Break character
length depends on the M bit in SCC1. As long as SBK is at logic 1, transmitter logic continuously loads
break characters into the transmit shift register. After software clears the SBK bit, the shift register finishes
transmitting the last break character and then transmits at least one logic 1. The automatic logic 1 at the
end of a break character guarantees the recognition of the start bit of the next character.
The SCI recognizes a break character when a start bit is followed by eight or nine logic 0 data bits and a
logic 0 where the stop bit should be.
Receiving a break character has these effects on SCI registers:
Sets the framing error bit (FE) in SCS1
Sets the SCI receiver full bit (SCRF) in SCS1
Clears the SCI data register (SCDR)
Clears the R8 bit in SCC3
Sets the break flag bit (BKF) in SCS2
May set the overrun (OR), noise flag (NF), parity error (PE), or reception-in-progress flag (RPF) bits
12.5.2.4 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 in SCC1. The preamble is a synchronizing idle character that begins every transmission.
If the TE bit is cleared during a transmission, the 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 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 is when the SCTE bit becomes set and just
before writing the next byte to the SCDR.
12.5.2.5 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.