Rabbit 2000 - Page 27

Designer’s Handbook 25
2. The top six bytes of the buffer (read from 0x7FFF8-0x7FFFF) are checked for an alter-
nating sequence of 0x55, 0xAA, 0x55, 0xAA, 0x55, 0xAA. If this is not found, the
block does not exist and an error (-2) is retured.
3. The ID block size (=SIZE) is determined from the first 4 bytes of the 16-byte buffer.
4. A block of bytes containing all fields from the start of the SysIDBlock struct up to but
not including the reserved field is read from flash at address 0x80000-SIZE, essentially
filling the SysIDBlock struct except for the reserved field (since the top 16 bytes have
been read earlier).
5. The CRC field is saved in a local variable, then set to 0x0000. A CRC check is then
cacculated for the entire ID block except the reserved field and compared to the saved
value. If they do not match, the block is considered invalid and an error (-3) is
returned. The CRC field is then restored.
The reserved field is avoided in the CRC check since its size may vary, depending on the
size of the ID block.
Table 2. The System ID Block
Offset from
start of block
Size (bytes) Description
00h 2ID block version number
02h 2Product ID
04h 2 Vendor ID
06h 7Timestamp (YY/MM/D/H/M/S)
0Dh 4Flash ID
11h 2Flash size (in 1000h pages)
13h 2Flash sector size
15h 2Number of sectors in flash
17h 2Flash access time (nanoseconds)
19h 4Flash ID, 2nd flash
1Dh 2Flash size (in 1000h pages), 2nd flash
1Fh 2Flash sector size, 2nd flash
21h 2Number of sectors in 2nd flash
23h 2Flash access time (nanoseconds), 2nd flash
25h 4RAM ID
29h 2RAM size (in 1000h pages)
2Bh 2RAM access time (nanoseconds)
2Dh 2CPU ID