[Main]
Name=OSCheckSilentLink
Type=Function
Subtype=ROM Call
Header Files=link.h
Definition=short OSCheckSilentLink (void);

[ROM Call]
Index=$24A

[Description]
Checks the link state.

[Explanation]
OSCheckSilentLink returns an integer which determines the link state. The meaning of the returned
value is:
<BR><BR>
<TABLE BORDER CELLPADDING="4">
<TR><TD VALIGN="TOP">0</TD><TD>None (the link is silent)</TD></TR>
<TR><TD VALIGN="TOP">1</TD><TD>A variable header or extended header is received</TD></TR>
<TR><TD VALIGN="TOP">2</TD><TD>A direct command, a screen dump, a request with size or a request is in progress</TD></TR>
<TR><TD VALIGN="TOP">3</TD><TD>The link is ready</TD></TR>
</TABLE>
<BR>
This function is called from high-level keyboard reading functions like
<A HREF="$$LINK(kbd.h/kbhit)">kbhit</A> and <A HREF="$$LINK(kbd.h/ngetchx)">ngetchx</A>, and if it returns
non-zero, <A HREF="$$LINK(link.h/OSLinkCmd)">OSLinkCmd</A> is called to process the received packet (as the
link is interrupt-driven, a packet may be received asynchronously, without the request from
the program itself). So, the TIOS can receive variables from the link whenever the program is
waiting for a keypress (used mainly when the calculator is in the Home Screen).

[References]
In=kbd.h/kbhit, kbd.h/ngetchx
Out=link.h/LIO_RecvData, link.h/OSLinkClose, link.h/OSLinkReset
