MCS3122 datasheet(5/26 Pages) MICROCHIP

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DS40001762A-page 5

MCS3122

3.0

MEMORY ORGANIZATION

MCS3122 has 64 bytes of configuration data. In

general, the Configuration bytes can be divided into

two categories: those options related to the Advanced

KEELOQ technology encoder and those related to the

transmitter and device operation.

3.1

Counter and Protection

The synchronization counter is read, checked for

integrity, updated (incremented) and saved back to

Flash during normal operation of the device. The

special operation prevents against data loss from

unexpected power loss. An 8-bit checksum is

calculated and stored alongside the synchronization

counter. The checksum is calculated as a two’s

complement checksum. If there is a mismatch, the

second copy of the synchronization counter is read

instead. Example 3-1 illustrates how to compute this

value.

EXAMPLE 3-1:

CHECKSUM CALCULATION

TABLE 3-1:

CONFIGURATION REGISTERS

Address

Size (Bytes)

Description

0x00-0x02

Synchronization Counter, Copy A

0x03

Synchronization Counter Checksum

0x04-0x07

Reserved (set to 0xFF)

0x08-0x0A

Synchronization Counter, Copy B

0x0B

Reserved (set to 0xFF)

0x0C-0x0F

Seed Transmission Serial Number (usually set to 0xFFFFFFFF)

0x10-0x1F

Encryption Key

0x20-0x2F

Authorization Key

0x30-0x33

Serial Number

0x34-0x35

Transmitter Settings

0x36-0x37

Reserved (set to 0xFF)

0x38-0x3F

Seed Value

static uint8_t crc(const uint8_t* buffer, size_t len){

uint8_t bitcount;

uint8_t checksum = 0xFF;

while(len--)

{

c = c + *buffer++;

}

return 0-c;

}

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