INT 15 - MultiDOS Plus - REQUEST RESOURCE SEMAPHORE
AH = 01h
AL = semaphore number (00h-3Fh)
Return: AH = status
00h successful
02h invalid semaphore number
Notes:  if the semaphore is not owned, ownership is assigned to the calling
task and the call returns immediately
if the semaphore is already owned by another task, the calling task
is placed on a queue for the semaphore and suspended until it can
become owner of the semaphore
semaphore 0 is used internally by MultiDOS to synchronize DOS access
SeeAlso: AH=10h"MultiDOS",AH=1Bh"MultiDOS"

See also: 1502

1501 - MultiDOS Plus - REQUEST RESOURCE SEMAPHORE