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MC68F375
QUEUED SERIAL MULTI-CHANNEL MODULE
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
6-52
mines the position of bit boundaries from transitions within the received waveform, and
adjusts sampling points to the proper positions within the bit period.
Table 6-29 shows theoretical baud rates for a 40-MHz system clock (the MC68F375
has a maximum system clock rate of 33 MHz).
6.8.7.4 Parity Checking
The PT bit in SCCxR1 selects either even (PT = 0) or odd (PT = 1) parity. PT affects
received and transmitted data. The PE bit in SCCxR1 determines whether parity
checking is enabled (PE = 1) or disabled (PE = 0). When PE is set, the MSB of data
in a frame (i.e., the bit preceding the stop bit) is used for the parity function. For trans-
mitted data, a parity bit is generated. For received data, the parity bit is checked. When
parity checking is enabled, the PF bit in the SCI status register (SCxSR) is set if a par-
ity error is detected.
Enabling parity affects the number of data bits in a frame, which can in turn affect
frame size. Table 6-30 shows possible data and parity formats.
6.8.7.5 Transmitter Operation
The transmitter consists of a serial shifter and a parallel data register (TDRx) located
in the SCI data register (SCxDR). The serial shifter cannot be directly accessed by the
Table 6-29 Examples of SCIx Baud Rates1
NOTES:
1. These rates are based on a 40-MHz system clock.
Nominal
Baud Rate
Actual
Baud Rate
Percent
Error
Value of
SCxBR
1,250,000.00
57,600.00
38,400.00
32,768.00
28,800.00
19,200.00
14,400.00
9,600.00
4,800.00
2,400.00
1,200.00
600.00
300.00
1,250,000.00
56,818.18
37,878.79
32,894.74
29,069.77
19,230.77
14,367.81
9,615.38
4,807.69
2,399.23
1,199.62
600.09
299.98
0.00
-1.36
0.39
0.94
0.16
-0.22
0.16
-0.03
0.02
-0.01
1
22
33
38
43
65
87
130
260
521
1042
2083
4167
Table 6-30 Effect of Parity Checking on Data Size
M
PE
Result
0
8 data bits
0
1
7 data bits, 1 parity bit
1
0
9 data bits
1
8 data bits, 1 parity bit
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