MC68HC908MR8 Datasheet, PDF (252/372 Pages) Motorola, Inc – Microcontrollers

Serial Communications Interface (SCI)
8-BIT DATA FORMAT
BIT M IN SCC1 CLEAR
POSSIBLE
PARITY
BIT
NEXT
START
START
BIT
BIT 0 BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 STOP BIT
BIT
START
9-BIT DATA FORMAT
BIT M IN SCC1 SET
POSSIBLE
PARITY
BIT
NEXT
START
BIT BIT 0 BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 BIT 8 STOP BIT
BIT
Figure 13-3. SCI Data Formats
13.4.2 Transmitter
Figure 13-4 shows the structure of the SCI transmitter.
13.4.2.1 Character Length
The transmitter can accommodate either 8-bit or 9-bit data. The state of
the M bit in SCI control register 1 (SCC1) determines character length.
When transmitting 9-bit data, bit T8 in SCI control register 3 (SCC3) is
the ninth bit (bit 8).
13.4.2.2 Character Transmission
During an SCI transmission, the transmit shift register shifts a character
out to the PTB1/TxD pin. The SCI data register (SCDR) is the write-only
buffer between the internal data bus and the transmit shift register.
To initiate an SCI transmission:
1. Enable the SCI by writing a logic 1 to the enable SCI bit (ENSCI)
in SCI control register 1 (SCC1).
2. Enable the transmitter by writing a logic 1 to the transmitter enable
bit (TE) in SCI control register 2 (SCC2).
3. Clear the SCI transmitter empty bit by first reading SCI status
register 1 (SCS1) and then writing to the SCDR.
4. Repeat step 3 for each subsequent transmission.
Technical Data
252
Serial Communications Interface (SCI)
MC68HC908MR8 — Rev 4.1
Freescale Semiconductor