Specifications

Developer’s Serial Bootloader, Rev. 13

FC protocol, version 1, M68HC908 implementation

Freescale Semiconductor12

The MCU sends this number of read bytes to the PC. If the CRC capability of serial protocol is enabled,

then the 16 bits(2 bytes) follows with CRC-CCITT checksum.

Figure 12. Read command

2.4.7 Quit command

The quit command (coded as ‘Q’, $51) has no address or data fields. Execution of bootloader code is

immediately finished, and the user code is started. No ACK ($FC) character is sent to the PC.

Figure 13. Quit command

2.4.8 Bootloader user table

The bootloader user table is a reprogrammable memory area intended for storage of bootloader-specific

data. This memory area is unavailable for the user program. For this table’s memory allocation, refer to

FC protocol, version 1, M68HC908 implementation.

3 FC protocol, version 1, M68HC908 implementation

This section describes features specific to the M68HC908 bootloader implementation. The memory

allocation is heavily MCU specific, so the meaning of all variables is explained in this section in detail.

Figure 14 shows the typical memory allocation for M68HC908 MCUs with the bootloader

preprogrammed. For example, the MC68HC908KX8 MCU memory map includes:

• 7680 bytes of FLASH memory ($E000–$FDFF)

• 192 bytes of random-access memory (RAM) ($0040–$00FF)

• 36 bytes of user-defined vectors ($FFDC–$FFFF)

R ($52)

PC TO MCU COMMAND

MCU TO PC RESPONSE

BINARY DATA

LENGTH

START

ADDRESS

CRC

Q ($51)

PC TO MCU COMMAND

MCU TO PC RESPONSE

CRC