equance of bytes sent in the data field of a command packet.
Command format is as follows:
<TABLE BORDER=1>
<TR><TH>Offset</TH><TH>Length</TH><TH>Description</TH></TR>
<TR><TD>0</TD><TD>1</TD><TD>Command code</TD></TR>
<TR><TD>1</TD><TD>1</TD><TD>Register number or subcode</TD></TR>
<TR><TD>2</TD><TD>variable</TD><TD>Optional argument</TD></TR>
</TABLE>

<P>
Five command codes are known:
<TABLE BORDER=1>
<TR><TH>Code</TH><TH>Argument</TH><TH>Description</TH></TR>
<TR><TD>0</TD><TD>int32</TD><TD