Sorry, but this is nowhere near 1977.
The Moor was pedestrianised in around '74. The Manpower Services Commission building was already being built across the bottom end of The Moor a year or two before that - maybe those cranes at the bottom of The Moor are for exactly that.
But the biggest giveaway, is the bus. It's still in the old Sheffield Transport livery - pale cream and navy blue. They became South Yorkshire Passenger Transport Executive (SYPTE), in maybe '72 or '73. 1974 at the very latest. That's when the livery became the pale cream and dirty brown colours.
My best guess for this photo would be 1972.
The old Suggs building and covered arcade on Pinstone Street has been demolished in this photo - LHS. Again, my guess would be 1972 for that. But if you want to be sure, that's where to begin.
EDIT: I take it all back. MSC Building did not open until! 1981, and The Moor was last used by traffic in 1979.
In the mid 70s, as school kids, we used to catch the number 4 bus back home from Paternoster Row, sometimes we walked up to Pinstone Street, or The Moor, where we could also catch any one of the 17, 24, 81, 82, or 83 bus routes.
I was quite certain that it was during my school years that buses down The Moor began taking that ridiculous detour around Manpower Services, and then later, the full detour down Charter Row. I later worked in the city centre for several years, and had the same choice of bus routes, so I am conflating the two periods and memories.