Trying to understand subroutines

[Gi Nattak]

Then, at CB/BE99 (talk to Cyan) I ran a subroutine (or, more recently, the Code:
C0 F0 01. If $1F0 is clear,
35 F0 00. Branch to 3F/F000
FE Return if set)

You must mean 00 F0 35? If you have it like you wrote it here, that would jump to CA/F035.