Specifications

Developer’s Serial Bootloader, Rev. 13
MCU slave software
Freescale Semiconductor54
MC68HC908GP and MC68HC908GR MCUs are primarily targeted for use with a low-cost 32.768 kHz
crystal. Because the frequency of the crystal is known, no calibration is performed, which saves MCU
memory. Therefore, these MCUs use the Known MCU communication speed method.
8.5 MC68HC908MR
MC68HC908MR MCUs are motor-control oriented members of the M68HC08 Family. The
MC68HC908MR MCUs have no on-chip FLASH programming routines available. Therefore, all FLASH
programming must be done by the bootloader.
The MC68HC908MR Family has a PLL (phase-locked loop) circuit that can multiply the crystal
frequency. Typically, a 4-MHz XTAL is used as the reference frequency. This implementation
demonstrates how the PLL circuit is initialized for 8 times the crystal frequency. Therefore, the source PLL
frequency is 32 MHz, and the bus frequency is 8 MHz.
Because the frequency of the crystal is known, no calibration is performed, which saves MCU memory.
Therefore, these MCUs use the Known MCU communication speed method.
8.6 MC68HC908EY
The code for MC68HC908GT and MC68HC908EY MCUs is similar to MC68HC908KX code, except for
the memory maps and ROM routine locations. One minor difference is that the MC68HC908GT Family
cannot use the CGMXCLK clock as the SCI module source. Therefore, the bus clock is the only possible
clock source.
8.7 MC68HC908QT/QY
MC68HC908QT/QY MCUs are the smallest members of the M68HC08 Family. They have a simple ICG
module (running on fixed frequency 12.8 MHz 25%). ROM routines are available.
There are several spare FLASH locations (mainly among unused interrupt vectors) also used for storing
the bootloader code.
8.7.1 SCI Application Program Interface (SCIAPI)
Software SCI communication is implemented on MC68HC908QT/QY, MC68HC908JK/JL, and
MC68HC908LB MCUs to reduce cost and enable the user code to call the SCI send and receive routines
(with certain limitations). The bootloader code now implements SCIAPI, which is the defined way to call
the SCI send and receive routines.
The detailed information, implementation notes, and limitations are provided in the
sci.h file (of the
QTQY folder). This file is the only resource that must be included in the user C code. The calling
convention and overall usage is described in this file, too. The main limiting factor for most applications
will be that the SCI receive routine is a blocking one. This means that routines will not return until an SCI
character is received. The 16-bit timer registers are also manipulated. Some applications will use this code
without problems.