M68HC08 datasheet(80/172 Pages) FREESCALE

80 / 172 page

Monitor ROM (MON)

MC68HC908JL3E Family Data Sheet, Rev. 3

Freescale Semiconductor

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

7.3.6 Commands

The monitor ROM uses the following commands:

•

READ (read memory)

•

WRITE (write memory)

•

IREAD (indexed read)

•

IWRITE (indexed write)

•

READSP (read stack pointer)

•

RUN (run user program)

BIT 5

START

BIT

BIT 0

BIT 1

STOP

BIT

START

BIT

BIT 2

BIT 3

BIT 4

BIT 6

BIT 7

START

BIT

BIT 0

BIT 1

STOP

BIT

START

BIT

BIT 2

$A5

BREAK

BIT 3

BIT 4

BIT 5

BIT 6

BIT 7

ADDR. HIGH

READ

ADDR. HIGH

ADDR. LOW

DATA

ECHO

SENT TO

MONITOR

RESULT

MISSING STOP BIT

TWO-STOP-BIT DELAY BEFORE ZERO ECHO

M68HC08 Datasheet(PDF) 80 Page - Freescale Semiconductor, Inc

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