24 Dec
2015
24 Dec
'15
11:33 p.m.
Noel is correct. The code sticks a number that’s big enough in the byte record count
register and then does a command which is
800 bpi 9 track READ and GO. The code makes use of the fact that after a bus reset the
memory address register is zero.
As long as you stick a number in the BRC that is bigger than the the record size on the
tape (and not bigger than the available memory on your system),
it will work.
777 is indeed BR .
It loads the first (assuming the tape is rewound) record into memory at location zero.
You then start the processor at zero to load that bootstrap program which does the rest of
the magic.