OSWORD &99
OSWORD &99 (153) Perform BeebLink request
On entry: XY?0 =inward control block size XY?1 =returned control block size XY?2 =command XY?3 =sub-command/returned status XY!4... On exit: XY?2 =&00 if call actioned XY?3 =returned status XY!4...