MC68HC908AT32 Datasheet, PDF (120/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

Monitor ROM (MON)
12.3.2 Data Format
Communication with the monitor ROM is in standard non-return-to-zero (NRZ) mark/space data format.
See Figure 12-2 and Figure 12-3.
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
START
BIT
BIT 0 BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 STOP BIT
BIT
Figure 12-2. 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 12-3. Sample Monitor Waveforms
STOP
BIT
STOP
BIT
NEXT
START
BIT
NEXT
START
BIT
12.3.3 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
READ
READ
ADDR. HIGH ADDR. HIGH ADDR. LOW ADDR. LOW
DATA
ECHO
RESULT
Figure 12-4. Read Transaction
12.3.4 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
MC68HC908AT32 Data Sheet, Rev. 3.1
120
Freescale Semiconductor