MC9S08EL32 Datasheet, PDF (205/356 Pages) Freescale Semiconductor, Inc – 8-Bit HCS08 Central Processor Unit (CPU)

The SLIC clock is the same as the CPU bus clock. The module is designed to provide better than 1% bit
rate accuracy at the lowest value of the SLIC clock frequency and the accuracy improves as the SLIC clock
frequency is increased. For this reason, it is advantageous to choose the fastest SLIC clock which is still
within the acceptable operating range of the SLIC.Because the SLIC may be used with MCUs with internal
oscillators, the tolerance of the oscillator must be taken into account to ensure that SLIC clock frequency
does not exceed the bounds of the SLIC clock operating range. This is especially important if the user
wishes to use the oscillator untrimmed, where process variations might result in MCU frequency offsets
of ±25%.
The acceptable range of SLIC clock frequencies is 2 to 20 MHz to guarantee LIN operations with greater
than 1.5% accuracy across the 1–20 kbps range of LIN bit rates. The user must ensure that the fastest
possible SLIC clock frequency never exceeds 20 MHz or that the slowest possible SLIC clock never falls
below 2 MHz under worst case conditions. This would include, for example, oscillator frequency
variations due to untrimmed oscillator tolerance, temperature variation, or supply voltage variation.
To initialize the SLIC module into LIN operating mode, the user must perform the following steps prior
to needing to receive any LIN message traffic. These steps assume the MCU has been reset either by a
power-on reset (POR) or any other MCU reset mechanism.
The steps for SLIC Initialization for LIN operation are:
1. Write SLCC1 to clear INITREQ.
2. When INITACK = 0, write SLCC1 & SLCC2 with desired values for:
a) SLCWCM — Wait clock mode.
3. Write SLCC2 to set up prescalers for:
a) RXFP — Digital receive filter clock prescaler.
4. Enable the SLIC module by writing SLCC2:
a) SLCE = 1 to place SLIC module into run mode.
b) BTM = 0 to disable byte transfer mode.
5. Write SLCC1 to enable SLIC interrupts (if desired).
12.6.6.2 Byte Transfer Mode Initialization
Bit rate synchronization is handled automatically in LIN mode, using the synchronization data contained
in each LIN message to derive the desired bit rate. In byte transfer mode (BTM = 1); however, the user
must set up the bit rate for communications using SLCBT.
More information on byte transfer mode is described in Section 12.6.16, “Byte Transfer Mode Operation,”
including the performance parameters on recommended maximum speeds, bit time resolution, and
oscillator tolerance requirements.
After the desired settings of bit time are determined, the SLIC Initialization for BTM operation is virtually
identical to that of LIN operation.
The steps are:
1. Write SLCC1 to clear INITREQ.
MC9S08EL32 Series and MC9S08SL16 Series Data Sheet, Rev. 3
Freescale Semiconductor
207