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Description MSB 14-Bit word LSB
RETLW Return with literal in W 11 01xx kkkk kkkk
where xx can be replaced by 00 and k are data bits, i.e. serial number byte
Opcode of RETLW instruction is hexadecimal 34KKH where kk is data Byte (serial number
byte)
Let’s assume we want to write serial number 1234ABCDH as part of four RETLW instructions
to device PIC. The highest Byte of serial number is the most significant Byte. We want to write
the serial number to device program memory at address 40H. Serial number split us very
useful in this situation. Serialization without serial number split will write the following number
to buffer and device:
Address
Data
0000080 CD AB 34 12 xx xx xx xx xx xx xx xx xx xx xx xx
Note: Address 80H is because buffer has byte organization and PIC has word organization so
it has equivalent program memory address 40H. When buffer has word organization x16, the
address will be 40H and number 1234ABCDH will be placed to buffer as following:
Address
Data
0000040 ABCD 1234 xxxx xxxx xxxx xxxx xxxx xxxx
We want to use RETLW instruction so buffer has to be:
Address
Data
0000040 34CD 34AB 3434 3412 xxxx xxxx xxxx xxxx
We can do this by following steps:
A) write four RETLW instructions at address 40H to main buffer (this can be done by hand
editing buffer or by loading file with proper content). The bottom 8 bits of each RETLW
instruction are not important now, because serialization will write correct serial number bytes at
bottom 8 bits of each RETLW instruction.
The buffer content before starting device program will look for example as following:
Address
Data
0000040 3400 3400 3400 3400 xxxx xxxx xxxx xxxx
8 bits of each RETLW instructions are zeros, they can have any value.
B) Set the serialization options as following:
S/N size:
4 Bytes
Address: 40H
Start value: 1234ABCDH
Step: 1
S/N mode: BIN
Style: HEX
Save to buffer: LS Byte first
Split serial number: checked
Split gap: 1 byte(s)
S/N fragment size: 1 byte(s)