Datasheet

Functional Description
MC68HC812A4 Data Sheet, Rev. 7
Freescale Semiconductor 155
14.5 Functional Description
The SCI allows full-duplex, asynchronous, NRZ serial communication between the MCU and remote
devices, including other MCUs. The SCI transmitter and receiver operate independently, although they
use the same baud rate generator. The CPU monitors the status of the SCI, writes the data to be
transmitted, and processes received data.
14.5.1 Data Format
The SCI uses the standard NRZ mark/space data format illustrated in Figure 14-3.
Figure 14-3. SCI Data Formats
Each data character is contained in a frame that includes a start bit, eight or nine data bits, and a stop bit.
Clearing the M bit in SCI control register 1 configures the SCI for 8-bit data characters. A frame with eight
data bits has a total of 10 bits. Setting the M bit configures the SCI for 9-bit data characters. A frame with
nine data bits has a total of 11 bits.
Setting the M bit configures the SCI for 9-bit data characters. The ninth data bit is the T8 bit in SCI data
register high (SCDRH). It remains unchanged after transmission and can be used repeatedly without
rewriting it. A frame with nine data bits has a total of 11 bits.
Table 14-1. Example 8-Bit Data Formats
Start Bit Data Bits Address Bit Parity Bit Stop Bit
18001
170 2
17011
17
1
(1)
1. The address bit identifies the frame as an address character. See 14.5.4.6
Receiver Wakeup.
1
Table 14-2. Example 9-Bit Data Formats
Start Bit Data Bits Address Bit Parity Bit Stop Bit
19001
180 2
18011
18
1
(1)
1. The address bit identifies the frame as an address character. See 14.5.4.6
Receiver Wakeup.
1
BIT 5
START
BIT
BIT 0 BIT 1
NEXT
STOP
BIT
START
BIT
9-BIT DATA FORMAT
BIT 2 BIT 3 BIT 4 BIT 6 BIT 7
PARITY
OR DATA
BIT
PARITY
OR DATA
BIT
BIT M IN SCCR1 SET
8-BIT DATA FORMAT
BIT M IN SCCR1 CLEAR
BIT 5BIT 0 BIT 1 BIT 2 BIT 3 BIT 4 BIT 6 BIT 7
BIT 8
STOP
BIT
NEXT
START
BIT
START
BIT