Unfortunately the D777 ROM is unlike any of the other NEC chips I've decapped. There are actually 2 ROM areas: a smaller one at top center with 50 rows of 114 bits, and a larger one across the bottom of the die with 64 rows of 360 bits. The smaller one has 7 columns of 16 bits and one column of 2 bits. The larger one has 24 columns alternating between 14 and 16 bits.
I transcribed both of them visually:www.seanriddle.com/d777_1_raw.bin
for the smaller one and www.seanriddle.com/d777_2_raw.bin
for the larger one.
Since 114 isn't divisible by 8, the first file has 50x15 bytes; each row has 6 bits of padding added to the end. I also rotated the 1st ROM array 180 degrees before transcribing so that the address decoding for the 2 ROM areas had the same orientation.
Because I dumped these visually, there are likely a few errors, so please double-check them