It is not possible to read from all the internal registers, this table shows the read/write status of each register for each type:
{|{{Prettytable|width: 700px; font-size: 2em;}}class="wikitable"|!rowspan=2|''Register Index''||!rowspan=2|''Register Name''||!colspan=3|''Type''
|-
|!0||!1 & 2||!3 & 4
|-
|0||Horizontal Total (-1)||colspan=3 style="text-align: center;"|Write Only