Datasheet

Monitor ROM (MON)
MC68HC908JL3E Family Data Sheet, Rev. 4
76 Freescale Semiconductor
7.3.3 Data Format
Communication with the monitor ROM is in standard non-return-to-zero (NRZ) mark/space data format.
(See Figure 7-3 and Figure 7-4.)
Figure 7-3. Monitor Data Format
Figure 7-4. Sample Monitor Waveforms
The data transmit and receive rate can be anywhere from 4800 baud to 28.8k-baud. Transmit and receive
baud rates must be identical.
7.3.4 Echoing
As shown in Figure 7-5, the monitor ROM immediately echoes each received byte back to the PTB0 pin
for error checking.
Figure 7-5. Read Transaction
Any result of a command appears after the echo of the last byte of the command.
7.3.5 Break Signal
A start bit followed by nine low bits is a break signal. (See Figure 7-6.) When the monitor receives a break
signal, it drives the PTB0 pin high for the duration of two bits before echoing the break signal.
Figure 7-6. Break Transaction
BIT 5
START
BIT
BIT 0 BIT 1
NEXT
STOP
BIT
START
BIT
BIT 2 BIT 3 BIT 4 BIT 6 BIT 7
BIT 5
START
BIT
BIT 0 BIT 1
NEXT
STOP
BIT
START
BIT
BIT 2 BIT 3 BIT 4 BIT 6 BIT 7
START
BIT
BIT 0 BIT 1
NEXT
STOP
BIT
START
BIT
BIT 2
$A5
BREAK
BIT 3 BIT 4 BIT 5 BIT 6 BIT 7
ADDR. HIGHREADREAD ADDR. HIGH ADDR. LOW ADDR. LOW DATA
ECHO
SENT TO
MONITOR
RESULT
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
MISSING STOP BIT
TWO-STOP-BIT DELAY BEFORE ZERO ECHO