Hello
I am glad :-)
It is correct, TDS540A use 28F020 flash, 3 MB Firmware.
NVSRAM on TDS5xxA is uniquie. Only this serie use DS1650 (512kb ) for calibration data, not DS1245 (128kb) by old serie and DS1486 (128kb include data & time) by new serie.
But i haven't this serie, -> i don't know , which address have this 512kb NVSRAM-space. Probably address range 0x0400 0000 to 0x0407 FFFF
Can i get this nvsram backup ? I want check. (or you should found 12345678 hexdezimal at 0x10 Address of NVSRAM Dump)
Which GPIB Adapter did you use?