TN-5916 FIRMWARE UPGRADE NOTES
Starting with TN-5916 firmware v4.0, digital signatures are now supported to 
enhance integrity checks and prevent exploitation from forged firmware. Because 
earlier firmware versions did not implement a digital signature algorithm, an 
intermediate firmware version must be installed before upgrading your TN-5916 
to firmware v4.0 or higher.

UPGRADING TN-5916 TO FIRMWARE v4.0 OR HIGHER:
Install the TN-5916 intermediate firmware v3.99.1 first, then upgrade your 
device to the desired firmware version.

DOWNGRADING TN-5916 FROM FIRMWARE v4.0 OR HIGHER TO v3.x OR LOWER:
Install the TN-5916 intermediate firmware v3.99.3 first, then downgrade your
device to the desired firmware version.
