
Serial Communications Interface Module (SCI)
General Release Specification
MC68HC(7)08LN56 — Rev. 2.0
208
Serial Communications Interface Module (SCI)
MOTOROLA
NONDISCLOSURE
AGREEMENT
REQUIRED
Setting the DMATE bit enables the SCTE bit to generate transmitter
DMA service requests and disables transmitter CPU interrupt requests.
When the transmit shift register is not transmitting a character, the
PTE5/TxD pin goes to the idle condition, logic one. If at any time
software clears the ENSCI bit in SCI control register 1 (SCC1), the
transmitter and receiver relinquish control of the port E pins.
12.5.2.3 Break Characters
Writing a logic one to the send break bit, SBK, in SCC2 loads the
transmit shift register with a break character. A break character contains
all logic zeros 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 one, 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 one. The
automatic logic one 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 zero data bits and a logic zero where the stop bit
should be. Receiving a break character has the following 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 ones 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.