MC68HC908QL4 Datasheet, PDF (166/226 Pages) Motorola, Inc – Microcontrollers

Slave LIN Interface Controller (SLIC) Module
Desired Bit Rate:
57,600 bps
External Crystal Frequency: 9.8304 MHz
1 Second ₌ 17.36111 ms
57,600 Bits
1 Bit
1 Second
4 CGMXCLK Period
406.90 ns
X
=
9,830,400 CGMXCLK Periods
1 SLIC Clock Period
1 SLIC Clock Period
17.36111 ms
1 SLIC Clock Period
42.67 SLIC Clock Periods
1 Bit
X
406.90 ns
=
1 Bit
Therefore, the closest SLCBT value would be 42 SLIC clocks (SLCBT = 0x002A).
Figure 14-19. SLCBT Value Calculation Example 2
Desired Bit Rate:
15,625 bps
External Crystal Frequency: 8.000 MHz
1 Second
64 ms
=
15,625 Bits
1 Bit
1 Second
4 CGMXCLK Period
500 ns
X
=
8,000,000 CGMXCLK Periods
1 SLIC Clock Period
1 SLIC Clock Period
64 ms
1 SLIC Clock Period
128 SLIC Clock Periods
X
=
1 Bit
500 ns
1 Bit
Therefore, the closest SLCBT value would be 128 SLIC clocks (SLCBT = 0x0080).
Figure 14-20. SLCBT Value Calculation Example 3
Desired Bit Rate:
9.615 bps
External Crystal Frequency: 8.000 MHz
1 Second
104.004 ms
=
9,615 Bits
1 Bit
1 Second
4 CGMXCLK Period
500 ns
X
=
8,000,000 CGMXCLK Periods
1 SLIC Clock Period
1 SLIC Clock Period
104.004 ms
1 SLIC Clock Period
208.008 SLIC Clock Periods
X
=
1 Bit
500 ns
1 Bit
Therefore, the closest SLCBT value would be 42 SLIC clocks (SLCBT = 0x00D0).
Figure 14-21. SLCBT Value Calculation Example 4
This resolution affects the sampling accuracy of the SLIC module on receiving bytes, but only as far as
locating the sample point of each bit within a given byte. The best sample point of the bit may be off by
as much as one SLIC clock period from the exact center of the bit, if the proper SLCBT value for the
desired bit rate is an odd number of SLIC clock periods.
MC68HC908QL4 Data Sheet, Rev. 7
166
Freescale Semiconductor