AN2295 Freescale Semiconductor / Motorola, AN2295 Datasheet - Page 41

• Manufacturer Part Number: AN2295
• Description: Developers Serial Bootloader for M68HC08 and HCS08 MCUs
• Manufacturer: Freescale Semiconductor / Motorola

MCU Slave Software
MC68HC908GT
MC68HC908EY
The code for MC68HC908GT and MC68HC908EY MCUs is similar to the
MC68HC908KX
code, except
for the memory maps and ROM routine locations. One minor difference is that MC68HC908GT Family
cannot use the CGMXCLK clock as the SCI module source. Thus the bus clock is the only possible clock
source.
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) that are also used for
storing the bootloader code.
Single-Wire Communication
Because of the small number of pins on MC68HC908QT devices, the single-wire SCI version has been
developed to keep the number of pins that are occupied by communication to a minimum.
Figure 28
illustrates an example single-wire RS-232 interface. The single-wire option has been ported to
MC68HC908JK/JL and MC68HC908LB bootloader because they use a software SCI also.
V
DD
10k
RXD
RS-232
MC68HC908QT/QY
TTL/232 SHIFTER
CONNECTION
MCU
TXD
Figure 28. Example Single-Wire Schematic
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 so-called SCIAPI which is the defined way
to call the SCI send and receive routines.
sci.h
The details, implementation notes, and limitations are provided in the
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 manipulated also. Some applications will use this code without problems.
Developer’s Serial Bootloader for M68HC08 and HCS08 MCUs, Rev. 6
Freescale Semiconductor
41