Serial Communications Interface Module (SCI)
Functional Description
MC68HC908MR16/MC68HC908MR32 — Rev. 4.0 Advance Information
MOTOROLA Serial Communications Interface Module (SCI) 281
14.4.1 Data Format
The SCI uses the standard non-return-to-zero mark/space data format
illustrated in Figure 14-3.
Figure 14-3. SCI Data Formats
14.4.2 Transmitter
Figure 14-4 shows the structure of the SCI transmitter.
14.4.2.1 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).
14.4.2.2 Character Transmission
During an SCI transmission, the transmit shift register shifts a ch aracter
out to the PTF5/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.
BIT 5
START
BIT BIT 0 BIT 1
NEXT
STOP
BIT
START
BIT
8-BIT DATA FORMAT
BIT M IN SCC1 CLEAR
START
BIT BIT 0
NEXT
STOP
BIT
START
BIT
9-BIT DATA FORMAT
BIT M IN SCC1 SET
BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 BIT 8
BIT 2 BIT 3 BIT 4 BIT 6 BIT 7
POSSIBLE
PARITY
BIT
POSSIBLE
PARITY
BIT