Bootloader Data Stream Structure
In 8-bit mode, the least significant byte (LSB) of the word is sent first followed by the most significant byte
(MSB). For 32-bit values, such as a destination address, the most significant word (MSW) is loaded first,
followed by the least significant word (LSW). The bootloaders take this into account when loading an 8-bit
data stream.
Table 2-4. LSB/MSB Loading Sequence in 8-Bit Data Stream
Byte Contents
LSB (First Byte of 2) MSB (Second Byte of 2)
1 2 LSB: AA (KeyValue for memory width = 8 bits) MSB: 08h (KeyValue for memory width = 8 bits)
3 4 LSB: Register initialization value or reserved MSB: Register initialization value or reserved
5 6 LSB: Register initialization value or reserved MSB: Register initialization value or reserved
7 8 LSB: Register initialization value or reserved MSB: Register initialization value or reserved
... ... ... ...
... ... ... ...
17 18 LSB: Register initialization value or reserved MSB: Register initialization value or reserved
19 20 LSB: Upper half of Entry point PC[23:16] MSB: Upper half of entry point PC[31:24] (Always 0x00)
21 22 LSB: Lower half of Entry point PC[7:0] MSB: Lower half of Entry point PC[15:8]
23 24 LSB: Block size in words of the first block to load. If the MSB: block size
block size is 0, this indicates the end of the source
program. Otherwise another block follows. For example, a
block size of 0x000A would indicate 10 words or 20 bytes
in the block.
25 26 LSB: MSW destination address, first block Addr[23:16] MSB: MSW destination address, first block Addr[31:24]
27 28 LSB: LSW destination address, first block Addr[7:0] MSB: LSW destination address, first block Addr[15:8]
29 30 LSB: First word of the first block being loaded MSB: First word of the first block being loaded
... ... ... ...
... ... ... ...
. . LSB: Last word of the first block to load MSB: Last word of the first block to load
. . LSB: Block size of the second block MSB: Block size of the second block
. . LSB: MSW destination address, second block Addr[23:16] MSB: MSW destination address, second block
Addr[31:24]
. . LSB: LSW destination address, second block Addr[7:0] MSB: LSW destination address, second block Addr[15:8]
. . LSB: First word of the second block being loaded MSB: First word of the second block being loaded
... ... ... ...
... ... ... ...
. . LSB: Last word of the second block MSB: Last word of the second block
. . LSB: Block size of the last block MSB: Block size of the last block
. . LSB: MSW of destination address of last block Addr[23:16] MSB: MSW destination address, last block Addr[31:24]
. . LSB: LSW destination address, last block Addr[7:0] MSB: LSW destination address, last block Addr[15:8]
. . LSB: First word of the last block being loaded MSB: First word of the last block being loaded
... ... ... ...
... ... ... ...
. . LSB: Last word of the last block MSB: Last word of the last block
n n+1 LSB: 00h MSB: 00h - indicates the end of the source
SPRU722C – November 2004 – Revised October 2006 Bootloader Features 27
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