Specifications

MCU slave software
Developer’s Serial Bootloader, Rev. 13
Freescale Semiconductor 55
8.7.2 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 occupied by communication to a minimum. Figure 36 illustrates an
example single-wire RS-232 interface. The single-wire option has been ported to MC68HC908JK/JL and
MC68HC908LB bootloader because they also use a software SCI.
Figure 36. Example single-wire schematic
The bootloader’s master side must be informed that the single-wire communication is used. This can be
done by calling the hc08sprg.exe software. Use the following extended calling convention:
hc08sprg.exe 1:S filename.s19
where, 1 specifies which COM port is used for communication and S stands for single-wire.
Original (old) format: hc08sprg.exe 1 filename.s19
Now defaults to: hc08sprg.exe 1:D filename.s19
where, D stands for dual-wire mode. The bootloader master can also detect the presence of a single-wire
interface if called:
hc08sprg.exe 1:? filename.s19
The detection is only possible if the serial interface (mainly the level shifter) is powered up and working
before the bootloading process starts. Because this is not usually the case, always specify the bootloading
mode by including either “:S” or “:D” in the parameter.
8.8 MC68HC908LJ
MC68HC908LJ MCUs are members of the M68HC08 Family used to drive LCD displays.
MC68HC908LJ MCUs have the ROM on-chip FLASH programming routines available. The calling
convention is slightly different from other M68HC08s (see MC68HC908LJ data sheet, monitor ROM
section).
MC68HC908LJ MCUs are primarily targeted to 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.
TTL/232 SHIFTER
V
DD
RS-232
CONNECTION
TXD
RXD
MC68HC908QT/QY
10k
MCU