#: 3947 S3/Languages
    29-May-90  18:15:32
Sb: #3917-C and JOoysticks
Fm: Bruce MacKenzie 71725,376
To: TONY CAPPELLINI 76370,2104 (X)

Oh, you have done some assembly work.  Those '$' as in 'os9 I$Write' are op
system calls which translate as 'SWI   ;FCB code' in standard 6809 assembler. 
'I$Write' is a symbol defined in os9defs and is equal to the system call code. 
What you do is load up the registers CPU with the appropriate values as
documented in the tech manual, execute the sys call with the 'os9' psuedo op,
the op system does what it does and then returns to calling program with the
CPU registers modified as documented.  The C function _os9(code,reg) loads the
registers with the values contained in the structure pointed to by reg and then
calls the system call specified by code.  The structure for the register values
and symbols for the sys call codes are defined in os9.h.  You ought to list
os9.h and have a look at it.  This should make things clearer.