AN2295 Freescale Semiconductor / Motorola, AN2295 Datasheet - Page 31

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

Software-SCI Transmit Char Routine
A detailed description of the software-SCI transmit and receive subroutines is provided in this section.
They both are based on a 16-bit timer, and the output-compare event is polled in the background loop.
The source code for the two routines is shown in
variable is used. It contains the actual length of 1 bit at the current communication speed in 16-bit timer
clock cycles. This variable is initialized during the calibration phase (see
Freescale Semiconductor
INITIALIZE, FEED AND
SET BIT COUNTER
RUN 16-BIT TIMER
TXD PIN LOW
ENTER
TO 9
Developer’s Serial Bootloader for M68HC08 and HCS08 MCUs, Rev. 6
CHAR INTO CARRY FLAG
SHIFT-OUT TRANSMIT
Figure 20. Soft-SCI Transmit Char Routine
CLEAR TIMER FLAG
BITS AND TEST
TEST CARRY
TXD PIN LOW
DECREMENT
TIMER FLAG
TIMER FLAG
RECEIVED?
WAIT FOR
CLEAR
YES
= 0
SET
NO
≠ 0
Figure
TXD PIN HIGH
21. Other than a few counters, a 16-bit ONEBIT
Slave Frequency
CLEAR TIMER FLAG
TXD PIN HIGH
STOP TIMER
TIMER FLAG
TIMER FLAG
RECEIVED?
WAIT FOR
MCU Slave Software
EXIT
YES
Calibration).
NO
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