MC908QT4MPE datasheet(144/184 Pages) FREESCALE

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MC68HC908QY/QT Family Data Sheet, Rev. 5

144

Freescale Semiconductor

15.3.1.4 Data Format

Communication with the monitor ROM is in standard non-return-to-zero (NRZ) mark/space data format.

Transmit and receive baud rates must be identical.

Figure 15-13. Monitor Data Format

15.3.1.5 Break Signal

A start bit (logic 0) followed by nine logic 0 bits is a break signal. When the monitor receives a break signal,

it drives the PTA0 pin high for the duration of two bits and then echoes back the break signal.

Figure 15-14. Break Transaction

15.3.1.6 Baud Rate

The monitor communication baud rate is controlled by the frequency of the external or internal oscillator

and the state of the appropriate pins as shown in Table 15-1.

Table 15-1 also lists the bus frequencies to achieve standard baud rates. The effective baud rate is the

bus frequency divided by 256 when using an external oscillator. When using the internal oscillator in

forced monitor mode, the effective baud rate is the bus frequency divided by 335.

15.3.1.7 Commands

The monitor ROM firmware uses these commands:

•

READ (read memory)

•

WRITE (write memory)

•

IREAD (indexed read)

•

IWRITE (indexed write)

•

READSP (read stack pointer)

•

RUN (run user program)

Table 15-2. Mode Difference

Modes

Functions

Reset

Vector High

Reset

Vector Low

Break

Vector High

Break

Vector Low

SWI

Vector High

SWI

Vector Low

User

$FFFE

$FFFF

$FFFC

$FFFD

$FFFC

$FFFD

Monitor

$FEFE

$FEFF

$FEFC

$FEFD

$FEFC

$FEFD

BIT 5

START

BIT

BIT 1

STOP

BIT

START

BIT

BIT 2

BIT 3

BIT 4

BIT 7

BIT 0

BIT 6

MISSING STOP BIT

2-STOP BIT DELAY BEFORE ZERO ECHO

MC908QT4MPE Datasheet(PDF) 144 Page - Freescale Semiconductor, Inc

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