In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Jon Williams wrote:

As of version 1.2 we have added the ability to declare a subroutine to the compiler; this helps the programmer in two ways:

1) Subroutines can exist anywhere in memory now
2) The compiler will check for the proper number of parameters.

In one of the posts above I showed a the subroutine code for TX_BYTE.  Here's how that's declared to the compiler:

TX_BYTE    SUB    1, 2

The "1, 2" section tells the compiler that this subroutine requires one parameter, and could take two.  So if you do something like this:

  TX_BYTE aVal, bVal, cVal

The compiler will flag it as too many parameters.  Notice too that I didn't need to use GOSUB -- this is optional with declared subroutines and saves a bit of typing.  Really, it's like adding your own commands.

For an example, have a look at this [early] version of the Serial Inkjet Printer drive code. 

    [url=http://forums.parallax.com/forums/attach.aspx?a=4029]http://forums.parallax.com/forums/attach.aspx?a=4029[/url]

You'll see a bunch of declared subroutines -- some with no parameters, so with mandatory and optional parameters.

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