AN2575 Freescale Semiconductor / Motorola, AN2575 Datasheet - Page 2

• Manufacturer Part Number: AN2575
• Description: MC68HC908EY16 ESCI LIN Drivers
• Manufacturer: Freescale Semiconductor / Motorola

AN2575/D
MC68HC908EY16 Enhancements for LIN
2
NOTE:
With the exception of mask set errata documents, if any other Motorola
document contains information that conflicts with the information in the data
sheet, the data sheet should be considered to have the most current and
correct data.
The downside of using the ICG is that the frequency is not as accurate as that
of a crystal or resonator. Parametric spreads during manufacture result in an
overall untrimmed accuracy of ±25% from the specified nominal reference
frequency of 307.2 kHz. In many applications, this is acceptable and no
trimming is necessary. For LIN, however, greater accuracy is required. This
application note describes a method of achieving the required performance.
The MC68HC908EY16 includes an ESCI (enhanced serial communications
interface) module that incorporates three enhancements specifically for LIN
(compared with the standard SCI used on many other HC08 MCUs).
The ICG incorporates a digitally controlled oscillator (DCO) whose operation is
fully described in application note AN2498/D: Initial trimming of the
MC68HC908 ICG. The DCO uses registers DDIV and DSTG that are managed
by the ICG hardware to make automatic corrections to the frequency of the
clock. The actual output frequency is determined by the user via the ICGTR
and ICGMR registers. The output frequency is set with the multiplier register,
ICGMR. This register is set to 21 ($15) at reset, giving a default clock frequency
of 6.4512 MHz ±25% (21 times 307.2 kHz). The user can change this value as
required. In this application, a value of 64 is used to give a nominal bus
frequency of 4.9152 MHz.
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Freescale Semiconductor, Inc.
For More Information On This Product,
The recognition of a 13-bit break
A fractional-divide baud rate prescaler that allows fine adjustment of the
baud rate
An arbiter counter that has 10 bits (9 bits plus an overflow bit) and can
be used as a mini-timer to measure break and bit times
MC68HC908EY16 ESCI LIN Drivers
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