U6 and U7 are the CPU EPROMs for a Boonton 4200 pwr meter with opt 01A (GPIB) 
S/N 1590-17AE. U1 is the GPIB board EPROM

Firmware is listed as V

EPROM data is:

U6	314BC	2885	NEC 2732
U7	356BC	2885	NEC 2716
U1	322BC	2885	NEC 2716


The files are saved in Intel HEX format.