Advance Information MC68HC908MR16/MC68HC908MR32 — Rev. 4.0

282 Serial Communications Interface Module (SCI) MOTOROLA

Serial Communications Interface Module (SCI)
Figure 14-4. SCI TransmitterAt the start of a transmission, transmitter control logic automatically loads the transmit shift register with a preamble of logic 1s. After the preamble shifts out, control logic transfers the SCDR data into the transmit shift register. A logic 0 start bit automatically goes into the least significant bit (LSB) position of the transmit shift register. A logic 1 stop bit goes into the most significant bit (MSB) position.The SCI transmitter empty bit, SCTE, in SCS1 becomes set when the SCDR transfers a byte to the transmit shift register. The SCTE bit indicates that the SCDR can accept new data from the internal data bus. If the SCI transmit interrupt enable bit, SCTIE, in SCC2 is also set, the SCTE bit generates a transmitter CPU interrupt request.
PEN
PTY
H876543210L
11-BIT
TRANSMIT
STOP
START
T8
SCTE
SCTIE
TCIE
SBK
TC
fOP
PARITY
GENERATION
MSB
SCI DATA REGISTER
LOAD FROM SCDR
SHIFT ENABLE
PREAMBLE
ALL 1s
BREAK
ALL 0s
TRANSMITTER
CONTROL LOGIC
SHIFT REGISTER
TC
SCTIE
TCIE
SCTE
TRANS MITTE R CPU INTE RRUPT REQUEST
M
ENSCI
LOOPS
TE
PTF5/TxD
TXINV
INTERNAL BUS
÷ 4PRE-
SCALER
SCP1
SCP0
SCR2
SCR1
SCR0
BAUD
DIVIDER ÷ 16