# Setting Special Bits and Bytes

In the device frame of the main window, you can read/write or clear/set some bytes and bits.

The following table summarizes the main bits and bytes as well as their status (Read / Write).

Bit or Byte Name | Meaning | Status
Signature Bytes | Manufacturer ID + Device ID1+ Device ID2 + Device ID3 | R
Device Boot IDs | Bootloader ID1 + Bootloader ID2 | R
Hardware Byte |  | R
Bootloader Version |  | R
BLJB | Bootloader Jump Bit (part of Hardware Byte) | RW
X2 | X2 Mode Bit (part of Hardware Byte) | RW
BSB | Boot Status Byte | RW
EB | Extra Byte | RW
SBV | Software Boot Vector | RW
SSB | Software Security Byte | RW

In order to modify a byte value, simply type an hexadecimal value (without any 0x prefix) in the byte entry field; as soon as two valid characters are typed, the byte is written; no return key typing is necessary.

The BLJB is active low. Checking its checkbox in the device frame enables it.

For information about the way some of these bytes and bits control the microcontroller boot process, please read the device and the bootloader datasheets.