MC68HC08BD24 Datasheet, PDF (110/244 Pages) Motorola, Inc – HCMOS Microcontroller Unit

The data transmit and receive rate can be anywhere from 4800 baud to
28.8 kbaud. Transmit and receive baud rates must be identical.
9.4.3 Echoing
As shown in Figure 9-4, the monitor ROM immediately echoes each
received byte back to the PTA0 pin for error checking.
SENT TO
MONITOR
READ
READ ADDR. HIGH ADDR. HIGH ADDR. LOW ADDR. LOW DATA
ECHO
RESULT
Figure 9-4. Read Transaction
Any result of a command appears after the echo of the last byte of the
command.
9.4.4 Break Signal
A start bit followed by nine low bits is a break signal (see Figure 9-5).
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 9-5. Break Transaction
Technical Data
110
MC68HC08BD24 — Rev. 1.1
Freescale Semiconductor