7-BIT Sum Series User Manual page 13

When pressing and holding the Bootloader button, one should connect the device via USB A-A cable to the PC running Windows. After
being recognized by Windows OS, adapter switches into Bootloader mode which is confirmed with continuous pulsation of the Status LED.
The next required step is to launch on the connected Windows PC SumFlasher application that will update firmware of the adapter.
When application detects connected Sum adapter it will enable Open Hex File button. Firmware update procedure looks as follows:

One should press Open Hex File button and choose a file containing updated firmware image (which results in enabling
Programming and Reset Device buttons).

One should press Programming button and wait for the flashing process to complete.

After completion of the flashing process, one should press Reset Device button, which switches Sum back into normal operation
mode allowing its disconnecting from the PC.
Having followed the above procedure one can connect the adapter back to the Amiga
All files required for the updating procedure can be downloaded from
Sum
Status
Bootloader button and status LED location for SumCDTV
.
http://retro.7-bit.pl website.
Bootloader
13