MC68HC08AS32 Datasheet, PDF (258/280 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

16.3.1.2 Data Format
Communication with the monitor ROM is in standard non-return-to-zero (NRZ)
mark/space data format. (See Figure 16-7 and Figure 16-8.)
START
BIT
The data transmit and receive rate can be anywhere from 4800 baud to
28.8 kBaud. Transmit and receive baud rates must be identical.
NEXT
START
BIT 0 BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 STOP BIT
BIT
Figure 16-7. Monitor Data Format
$A5
BREAK
START
BIT
BIT 0 BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7
START
BIT
BIT 0 BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7
Figure 16-8. Sample Monitor Waveforms
STOP
BIT
STOP
BIT
NEXT
START
BIT
NEXT
START
BIT
16.3.1.3 Echoing
SENT TO
MONITOR
As shown in Figure 16-9, 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.
READ
READ
ADDR. HIGH ADDR. HIGH ADDR. LOW ADDR. LOW
DATA
ECHO
RESULT
Figure 16-9. Read Transaction
16.3.1.4 Break Signal
A start bit followed by nine low bits is a break signal. (See Figure 16-10.) 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
Data Sheet
258
01234567
01234567
Figure 16-10. Break Transaction
MC68HC08AS32 — Rev. 4.1
Freescale Semiconductor