MC68HC812A4 Datasheet, PDF (230/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Serial Communications Interface Module (SCI)
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 14-2. Example 9-Bit Data Formats
Start Bit Data Bits Address Bit Parity Bit Stop Bit
1
9
0
0
1
1
8
0
2
1
8
0
1
1
1
8
1⁽¹⁾
1
1. The address bit identifies the frame as an address character. See 14.6.4.6
Receiver Wakeup.
14.6.2 Baud Rate Generation
A 13-bit modulus counter in the baud rate generator derives the baud
rate for both the receiver and the transmitter. The value from 0 to 8191
written to the SBR12–SBR0 bits determines the module clock divisor.
The SBR bits are in the SCI baud rate registers (SCBDH and SCBDL).
The baud rate clock is synchronized with the bus clock and drives the
receiver. The baud rate clock divided by 16 drives the transmitter. The
receiver has an acquisition rate of 16 samples per bit time.
Baud rate generation is subject to two sources of error:
• Integer division of the module clock may not give the exact target
frequency.
• Synchonization with the bus clock can cause phase shift.
Table 14-3 lists some examples of achieving target baud rates with a
module clock frequency of 10.2 MHz.
MC68HC812A4 — Rev. 3.0
230
Serial Communications Interface Module (SCI)
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