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	<TITLE>TI-85 Link Protocol Guide - Packet formats</TITLE> 
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<P><B>TI-85 Link Protocol Guide v1.0</B> - Packet formats</P> 
<CENTER> 
<H2> 
<HR ALIGN="CENTER"> 
Packet Formats</H2> 
</CENTER> 
<P>Texas Instruments calculators always send data and responses in self-contained &quot;packets.&quot;<BR> 
Packets have the following format:<BR> 
<I>Note - all 2-byte integers are transmitted little-endian Intel-style (least significant byte first).</I></P> 
<P> 
<TABLE BORDER="1" CELLSPACING="0" WIDTH="92%"> 
	<TR> 
		<TH WIDTH="7%" BGCOLOR="#008800"><FONT COLOR="#FFFFFF">Offset</FONT></TH> 
		<TH WIDTH="8%" BGCOLOR="#008800"><FONT COLOR="#FFFFFF">Length</FONT></TH> 
		<TH WIDTH="85%" BGCOLOR="#008800"><FONT COLOR="#FFFFFF">Description</FONT></TH> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">0</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF">1 byte</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Machine ID byte</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">1</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF">1 byte</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Command ID byte</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">2</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF">2 bytes</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Length of data (see note below)</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">4</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF"><I>n</I> bytes</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Data (if attached)</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">4+<I>n</I></TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF">2 bytes</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Checksum (if data is attached)</TD> 
	</TR> 
</TABLE> 
<I>Note - The &quot;Length of data&quot; element may not be equal to zero if the packet contains no data. In this 
case, the Command ID byte will indicate that the packet contains no data.</I><p></P> 
<H4>The Machine ID Byte</H4> 
<P>The Machine ID byte identifies the machine that is sending the packet. It can have one of the following values: 
 
<TABLE BORDER="1" CELLSPACING="0" WIDTH="66%"> 
	<TR> 
		<TH WIDTH="13%" BGCOLOR="#DDDDDD">Value</TH> 
		<TH BGCOLOR="#DDDDDD">Description</TH> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">05h</TD> 
		<TD>Computer sending TI-85 data</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">85h</TD> 
		<TD>TI-85</TD> 
	</TR> 
</TABLE> 
<p></P> 
<H4>The Command ID Byte</H4> 
<P>The Command ID byte identifies the request or response that the machine is sending. It can have one of the following 
values:</P> 
<P> 
<TABLE BORDER="1" CELLSPACING="0" WIDTH="66%"> 
	<TR> 
		<TH WIDTH="22%" BGCOLOR="#DDDDDD">Value</TH> 
		<TH WIDTH="259" BGCOLOR="#DDDDDD">Description</TH> 
		<TH BGCOLOR="#DDDDDD">Data Included</TH> 
	</TR> 
	<TR> 
		<TD WIDTH="22%">06h</TD> 
		<TD WIDTH="259">Variable Header (VAR)</TD> 
		<TD>A standard <A HREF="#varheader">variable header</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="22%">09h</TD> 
		<TD WIDTH="259">Clear to send (CTS)</TD> 
		<TD><I>None</I></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="22%">15h</TD> 
		<TD WIDTH="259">Data packet (DATA)</TD> 
		<TD>Screenshot/variable/backup data</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="22%">36h</TD> 
		<TD WIDTH="259">Skip/Exit (SKIP/EXIT)</TD> 
		<TD>A one-byte rejection code (see codes below)</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="22%">56h</TD> 
		<TD WIDTH="259">Acknowledge (ACK)</TD> 
		<TD><I>None</I></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="22%">5Ah</TD> 
		<TD WIDTH="259">Checksum Error (ERR)<BR> 
			The previous packet must be sent again.</TD> 
		<TD><I>None</I></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="22%">6Dh</TD> 
		<TD WIDTH="259"><I>Silent</I> - Request Screenshot (SCR)</TD> 
		<TD><I>None</I></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="22%">92h</TD> 
		<TD WIDTH="259">End of Transmission (EOT)</TD> 
		<TD><I>None</I></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="22%">A2h</TD> 
		<TD WIDTH="259"><I>Silent</I> - Request Variable (REQ)</TD> 
		<TD>A NUL padded (fixed-length) <A HREF="#varheader">variable header</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="22%">C9h</TD> 
		<TD WIDTH="259"><I>Silent</I> - Request to Send Variable (RTS)</TD> 
		<TD>A SPC padded (fixed-length) <A HREF="#varheader">variable header</A></TD> 
	</TR> 
</TABLE> 
<p></P> 
<P>Rejection codes (used with Command ID 36h) can have one of the following values:</P> 
<P> 
<TABLE BORDER="1" CELLSPACING="0" WIDTH="66%"> 
	<TR> 
		<TH WIDTH="13%" BGCOLOR="#DDDDDD">Value</TH> 
		<TH BGCOLOR="#DDDDDD">Description</TH> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">01h</TD> 
		<TD>EXIT - The entire transmission has been cancelled.</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">02h</TD> 
		<TD>SKIP - The current variable has been skipped.</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">03h</TD> 
		<TD>OUT OF MEMORY (silent transmissions only) - The receiving calculator is out of memory.</TD> 
	</TR> 
</TABLE> 
<p></P> 
<H4>The Checksum</H4> 
<P>The checksum is a 16-bit value used to verify the integrity of the data in the packet. It only present if data 
is present.<BR> 
The checksum is calculated by taking the lower 16 bits of the sum of the data bytes, as shown below:</P> 
<PRE>int calculateChecksum(unsigned char* data, unsigned short datalength) { 
   unsigned short x, checksum; 
   for(x=0; x&lt;datalength; x++) { 
      checksum+=data[x];  //overflow automatically limits to 16 bits 
   } 
   return checksum; 
}</PRE> 
<CENTER> 
<H3> 
<HR ALIGN="CENTER"> 
<A NAME="varheader"></A>Variable Headers</H3> 
</CENTER> 
<P>A Variable header contains information about one variable in the calculator.<BR> 
Standard and padded variable headers have the following format:</P> 
<P> 
<TABLE BORDER="1" CELLSPACING="0" WIDTH="92%"> 
	<TR> 
		<TH WIDTH="7%" BGCOLOR="#008800"><FONT COLOR="#FFFFFF">Offset</FONT></TH> 
		<TH WIDTH="8%" BGCOLOR="#008800"><FONT COLOR="#FFFFFF">Length</FONT></TH> 
		<TH WIDTH="85%" BGCOLOR="#008800"><FONT COLOR="#FFFFFF">Description</FONT></TH> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">0</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF">2 bytes</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Size of actual variable data, in bytes</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">2</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF">1 byte</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Type ID Byte (see type ID's below)</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">3</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF">1 byte</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Size of variable name, in characters</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">4</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF"><I>n</I> bytes</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Variable name (not zero-terminated)</TD> 
	</TR> 
</TABLE> 
<I>Note: These bytes only make up the &quot;data&quot; section of the packet.</I><p></P> 
 
<P>A padded variable header will always be 12 bytes long. The unused bytes at the end are padded with space characters 
(20h) or NULLs (0h). The standard and padded formats for variable headers are interchangeable.</P> 
<H4><A NAME="vartypes"></A>The Type ID Byte</H4> 
<P>The type ID byte specifies the type of variable that is being transmitted. It can have one of the following 
values:</P> 
<P> 
<TABLE BORDER="1" CELLSPACING="0" WIDTH="66%"> 
	<TR> 
		<TH WIDTH="13%" BGCOLOR="#DDDDDD">Value</TH> 
		<TH BGCOLOR="#DDDDDD">Description (click for variable format)</TH> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">00h</TD> 
		<TD><A HREF="vars.html#real">Real Number</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">01h</TD> 
		<TD><A HREF="vars.html#complex">Complex Number</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">02h</TD> 
		<TD><A HREF="vars.html#vector">Real Vector</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">03h</TD> 
		<TD><A HREF="vars.html#vector">Complex Vector</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">04h</TD> 
		<TD><A HREF="vars.html#list">Real List</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">05h</TD> 
		<TD><A HREF="vars.html#list">Complex List</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">06h</TD> 
		<TD><A HREF="vars.html#matrix">Real Matrix</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">07h</TD> 
		<TD><A HREF="vars.html#matrix">Complex Matrix</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">08h</TD> 
		<TD><A HREF="vars.html#constant">Real Constant</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">09h</TD> 
		<TD><A HREF="vars.html#constant">Complex Constant</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">0Ah</TD> 
		<TD><A HREF="vars.html#equation">Equation</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">0Ch</TD> 
		<TD><A HREF="vars.html#string">String</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">0Dh</TD> 
		<TD><A HREF="vars.html#gdb">Function GDB</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">0Eh</TD> 
		<TD><A HREF="vars.html#gdb">Polar GDB</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">0Fh</TD> 
		<TD><A HREF="vars.html#gdb">Parametric GDB</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">10h</TD> 
		<TD><A HREF="vars.html#gdb">Differential Equation GDB</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">11h</TD> 
		<TD><A HREF="vars.html#picture">Picture</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">12h</TD> 
		<TD><A HREF="vars.html#program">Program</A></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">14h</TD> 
		<TD>Screenshot sent by PrtScrn <I>(See note below)</I></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">17h</TD> 
		<TD><A HREF="vars.html#window">Func: Function Window Settings</A><I> (See note below)</I></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">18h</TD> 
		<TD><A HREF="vars.html#window">Pol: Polar Window Settings</A><I> (See note below)</I></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">19h</TD> 
		<TD><A HREF="vars.html#window">Param: Parametric Window Settings</A><I> (See note below)</I></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">1Ah</TD> 
		<TD><A HREF="vars.html#window">DifEq: Differential Equation Window Settings</A><I> (See note below)</I></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">1Bh</TD> 
		<TD><A HREF="vars.html#window">ZRCL: Saved Window Settings</A><I> (See note below)</I></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">1Dh</TD> 
		<TD>Backup <I>(No meaningful name)</I></TD> 
	</TR> 
	<TR> 
		<TD WIDTH="13%">1Eh</TD> 
		<TD>Unknown (only used when requesting variables of unknown type)</TD> 
	</TR> 
</TABLE> 
<I>Note - If the Type ID is in the range 14h - 1Bh, then the name length byte has a value of 0 and the name field 
consists of a single 0 byte.</I><p></P> 
<H4><A NAME="backup"></A>Backup Header Format</H4> 
<P>If the type ID byte specifies a backup, the variable header takes the following 9-byte format:</P> 
<P> 
<TABLE BORDER="1" CELLSPACING="0" WIDTH="92%"> 
	<TR> 
		<TH WIDTH="7%" BGCOLOR="#008800"><FONT COLOR="#FFFFFF">Offset</FONT></TH> 
		<TH WIDTH="8%" BGCOLOR="#008800"><FONT COLOR="#FFFFFF">Length</FONT></TH> 
		<TH WIDTH="85%" BGCOLOR="#008800"><FONT COLOR="#FFFFFF">Description</FONT></TH> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">0</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF">2 bytes</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Size of first backup section, in bytes</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">2</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF">1 byte</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Type ID Byte (1Dh in this case)</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">3</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF">2 bytes</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Size of second backup section, in bytes</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">5</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF">2 bytes</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Size of third backup section, in bytes</TD> 
	</TR> 
	<TR> 
		<TD WIDTH="7%" BGCOLOR="#FFFFFF">7</TD> 
		<TD WIDTH="8%" BGCOLOR="#FFFFFF">2 bytes</TD> 
		<TD WIDTH="85%" BGCOLOR="#FFFFFF">Memory address of second section</TD> 
	</TR> 
</TABLE> 
<p></P> 
 
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