What is "H" in opcodes (very confused)

Question

In my computer organization class, we're learning opcodes, and i understand most of the opcodes, and the concepts of them, but seriously, theres no legend for what "H" is for example..

iadd

iadd1:mar=sp=sp-1;rd
iadd2: H =tos..

whats H??

x'D thanks!

Answer 1

H is a register name, not an opcode.

Hold (H)

This register holds data that is to be supplied to the left (A) input of the arithmetic logic unit. This is the only register that can perform this function.

http://dsearls.org/courses/C391OrgSys/SimHelp/HTML/IJVM_Register_Set.htm