DEMO9S08EL32 Freescale Semiconductor, DEMO9S08EL32 Datasheet - Page 227

BOARD DEMO FOR 9S08 EL MCU

DEMO9S08EL32

Manufacturer Part Number
DEMO9S08EL32
Description
BOARD DEMO FOR 9S08 EL MCU
Manufacturer
Freescale Semiconductor
Type
MCUr
Datasheets

Specifications of DEMO9S08EL32

Contents
Evaluation Board
Processor To Be Evaluated
MC9S08EL32
Data Bus Width
8 bit
Interface Type
RS-232, USB
Operating Supply Voltage
12 V
Silicon Manufacturer
Freescale
Core Architecture
HCS08
Core Sub-architecture
HCS08
Silicon Core Number
MC9S08
Silicon Family Name
S08EL
Rohs Compliant
Yes
For Use With/related Products
MC9S08EL32
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
SLCACT will only be cleared by the SLIC upon successful completion of a normal LIN message frame
(see
with an error condition or some source other than those cited in the SLCACT bit description, SLCACT
might remain set during an otherwise idle bus time. SLCACT will then clear upon the successful
completion of the next LIN message frame.
These mechanisms might result in SLCACT being set when it is safe (from the SLIC module perspective)
to trim the oscillator. However, SLCACT will only be clear when the SLIC considers it safe to trim the
oscillator.
In a particular system, it might also be possible to improve the opportunities for trimming by using system
knowledge and use of IMSG. If a message ID is known to be considered a “don’t care” by this particular
node, it should be safe to trim the oscillator during that message frame (provided that it is safe for the
application software as well). After the software has done an identifier lookup and determined that the ID
corresponds to a “don’t care” message, the software might choose to set IMSG. From that time, the
application software should have at least one byte time of message traffic in which to trim the oscillator
before that ignored message frame expires, regardless of the state of SLCACT. If the length of that ignored
message frame is known, that knowledge might also be used to extend the time of this oscillator trimming
opportunity.
Now that the mechanisms for recognizing when the SLIC module indicates safe oscillator trimming
opportunities are understood, it is important to understand how to derive the information needed to
perform the trimming.
The value in SLCBT will indicate how many SLIC clock cycles comprise one bit time and for any given
LIN bus speed, this will be a fixed value if the oscillator is running at its ideal frequency. It is possible to
use this ideal value combined with the measured value in SLCBT to determine how to adjust the oscillator
of the microcontroller.
The actual oscillator trimming algorithm is very specific to each particular implementation, and
applications might or might not require the oscillator even to be trimmed. The SLIC can maintain
communications even with input oscillator variation of ±50% (with 4 MHz nominal, that means that any
input clock into the SLIC from 2 MHz to 6 MHz will still guarantee communications). Because Freescale
internal oscillators are at least within ±25% of their nominal value, even when untrimmed, this means that
trimming of the oscillator is not even required for LIN communications. If the application can tolerate the
range of frequencies which might appear within this manufacturing range, then it is not necessary ever to
trim the oscillator. This can be a tremendous advantage to the customer, enabling migration to very
low-cost ROM devices which have no non-volatile memory in which to store the trim value.
Freescale Semiconductor
Section ,
“,” description for more detail). This means that in some cases, if a message frame terminates
Even though most internal oscillators are within ±25% before trimming,
they are stable at some frequency in that range, within at least ±5% over the
entire operating voltage and temperature range. The trimming operation
simply eliminates the offset due to factory manufacturing variations to
re-center the base oscillator frequency to the nominal value. Please refer to
the electrical specifications for the oscillator for more specific information,
as exact specifications might differ from module to module.
MC9S08EL32 Series and MC9S08SL16 Series Data Sheet, Rev. 3
NOTE
229

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