C509-L_97 SIEMENS [Siemens Semiconductor Group], C509-L_97 Datasheet - Page 245

• Manufacturer Part Number: C509-L_97
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

Bootstrap Loader
C509-L
10.2.2 Checksum Calculation
The external FLASH memory check in phase I uses a checksum algorithm, which is based on a
continuous addition and 8-bit-left-rotation of all relevant data bytes. The data in the corresponding
FLASH memory area is split into two parts, on which an extra checksum is built. This is done to
reach a maximum of data security. Checksum #1 is build by bytes at odd addresses and
checksum #2 is calculated with bytes at even addresses. The checksum calculation itself is
described in the flowchart in figure 10-5.
Figure 10-5
Flowchart of the Checksum Calculation for the external FLASH Memory
Semiconductor Group
10-7
1997-10-01