MC68HC08AS20 Datasheet, PDF (158/386 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

12.4.3 Echoing
As shown in Figure 12-4, the monitor ROM immediately echoes each
received byte back to the PTA0 pin for error checking.
Any result of a command appears after the echo of the last byte of the
command.
SENT TO
MONITOR
ECHO
READ
READ
ADDR. HIGH ADDR. HIGH ADDR. LOW ADDR. LOW
DATA
Figure 12-4. Read Transaction
RESULT
12.4.4 Break Signal
A start bit followed by nine low bits is a break signal. (See Figure 12-5.)
When the monitor receives a break signal, it drives the PTA0 pin high for
the duration of two bits before echoing the break signal.
MISSING STOP BIT
TWO-STOP-BIT DELAY BEFORE ZERO ECHO
01234567
01234567
Figure 12-5. Break Transaction
Advance Information
158
MC68HC08AS20 —Rev. 4.1
Freescale Semiconductor