About Download Mode:Download Mode is a state your phone can be in that allows you to flash firmware through Odin or other desktop software.
When in Download Mode, you will see a triangle with an Android image in it and it says "Downloading..."
If you are stuck on the 'Downloading..." screen, you can just remove and re-insert the battery then power the phone back on.
If you are flashing firmware while in download mode, then you unplug it or remove the battery, your phone probably won't turn on any more.
Download Mode is essentially the same as Bootloader Mode.
How To Access Download Mode for S2 :
4 Ways to do access download mode for
1-Button ComboTurn off and turn S2 Again by hold the Power button, Home button and volume down button
2-Reboot Application (requires root See here guide for rooting Galaxy S2)
3-USB Jig
4-CMD/Terminal
a-Install ADB
b-You must have
USB Drivers installed for your device.
c-Enable
USB Debugging on your device and plug it into your computer via USB cable.
d-Open CMD (windows) or Terminal (linux/mac). To open CMD, hold windows key, then press R, then type cmd.exe and press enter.
e-Type adb reboot download
Source :
Rooter15 ,
jakar