MC68HC908QL4 Datasheet, PDF (162/226 Pages) Motorola, Inc – Microcontrollers

Slave LIN Interface Controller (SLIC) Module
will resume. If the SLIC was in SLIC stop mode, SLCSV will indicate wakeup as the interrupt source so
that the user knows that the SLIC module brought the MCU out of stop or wait.
In a LIN system, a system message is generally sent to all nodes to indicate that they are to enter
low-power network sleep mode. After a node enters sleep mode, it waits for outside events, such as
switch or sensor inputs or network traffic to bring it out of network sleep mode. If the node using the SLIC
module is awakened by a source other than network traffic, such as a switch input, the LIN specification
requires this node to issue a wake-up signal to the rest of the network. The SLIC module supports this
feature using WAKETX in SLCC2. The user software may set this bit and one LIN wake-up signal is
immediately transmitted on the bus, then the bit is automatically cleared by the SLIC module. If another
wake-up signal is required to be sent, the user must set WAKETX again.
In a LIN system, the LIN physical interface can often also provide an output to the IRQ pin to provide a
wake-up mechanism on network activity. The physical layer might also control voltage regulation supply
to the MCU, cutting power to the MCU when the physical layer is placed in its low-power mode. The user
must take care to ensure that the interaction between the physical layer, IRQ pin, SLIC transmit and
receive pins, and power supply regulator is fully understood and designed to ensure proper operation.
14.9.12 Polling Operation
It is possible to operate the SLIC module in polling mode, if desired. The primary difference is that the
SLIC interrupt request should not be enabled (SLCIE = 0). The SLCSV will update and operate properly
and interrupt requests will be indicated with the SLCF flag, which can be polled to determine status
changes in the SLIC module. It is required that the polling rate be fast enough to ensure that SLIC status
changes be recognized and processed in time to ensure that all application timings can be met.
14.9.13 LIN Data Integrity Checking Methods
The SLIC module supports two different LIN-based data integrity options:
• The first option supports LIN 1.3 and older methods of checksum calculations.
• The second option supports an optional additional enhanced checksum calculation which has
greater data integrity coverage.
The LIN 1.3 and earlier specifications transmit a checksum byte in the “CHECKSUM FIELD” of the LIN
message frame. This CHECKSUM FIELD contains the inverted modulo-256 sum over all data bytes. The
sum is calculated by an “ADD with Carry” where the carry bit of each addition is added to the least
significant bit (LSB) of its resulting sum. This guarantees security also for the MSBs of the data bytes. The
sum of modulo-256 sum over all data bytes and the checksum byte must be ’0xFF’.
An optional checksum calculation can also be performed on a LIN data frame which is very similar to the
LIN 1.3 calculation, but with one important distinction. This enhanced calculation simply includes the
identifier field as the first value in the calculation, whereas the LIN 1.3 calculation begins with the least
significant byte of the data field (which is the first byte to be transmitted on the bus). This enhanced
calculation further ensures that the identifier field is correct and ties the identifier and data together under
a common calculation, ensuring greater reliability.
In the SLIC module, either checksum calculation can be performed on any given message frame by
simply writing or clearing CHKMOD in SLCDLC, as desired, when the identifier for the message frame is
decoded. The appropriate calculation for each message frame should be decided at system design time
and documented in the LIN description file, indicating to the user which calculation to use for a particular
identifier.
MC68HC908QL4 Data Sheet, Rev. 7
162
Freescale Semiconductor