Boot ROMMCF5253 Reference Manual, Rev. 1Freescale Semiconductor 19-519.2.3.2 Supported Commands• Store Immediate— The store immediate command causes the boot loader to read from the serial device and storethe data at the destination address as soon as a complete unit (1, 2 or 4 bytes) has been read.The unit size is defined in the lower nibble of the command word.• Execute— The execute command has no data associated to it. The address field contains the entry pointof the code to be executed. The byte count is 0. Upon reception of an execute command, theloader calls the routine at the specified address by means of a JSR instruction. If the calledroutine returns, the loader will continue and read the next boot record.19.2.4 IDE Boot Data FormatAn IDE boot record has the following structure:The load address provides the start location where the boot record will be stored within the MCF5253’smemory map, the execution address provides the entry point code execution will begin from after the bootrecord has been loaded into memory. The CRC allows the boot record to be validated before attempting tobegin code execution. The length of the boot record is described in number of sectors (512 bytes) itoccupies on the drive, up to a maximum of 256, making the maximum boot file size 131,060 bytes, 12bytes are required for the boot record.The boot record must be stored as the first three files in the root directory of a newly formatted FAT32device. The files have to be in a continuous cluster (single section) and named as IDEBOOT1.IDE,IDEBOOT2.IDE and IDEBOOT3.IDE.19.2.5 Boot Modes19.2.5.1 Boot From I 2C / SPI – Master ModeIn I 2C master mode, the boot loader reads data from a serial EEPROM/FLASH connected to I2C0 (SCL0and SDA0). The I2C address of the device must be 0b1010000x, as this address is standard for serialmemories. Only devices which use a 16-bit memory address are supported. The I2C clock speed is set at100KHz when the maximum crystal / external clock input is used (33.8688 MHz). The I 2C clock speedTable 19-5. Boot RecordsOffset # Bytes Description0 4 Load address in MCF5253 memory space4 4 Execution address8 2 Boot record CRC10 2 Length of record in sectors (max 256)12 – Data/Code section
