|Re: Viewing the full mantissa on a 41C|
Message #4 Posted by Andrés Rodríguez (Argentina) on 5 Nov 2005, 10:31 a.m.,
in response to message #2 by Vassilis Prevelakis
The decision to implement separate DSP and FIX/SCI/ENG instructions has to do with op-code space preservation. The HP 67 (as the HP 25 and others) used just one byte to encode each instruction, hence there are only 256 op-codes available. With a rather rich set of instructions, you need to be careful in order to avoid running out of possible op-codes. The separate option uses just 13 op-codes for all display formats (FIX, SCI, ENG, DSP 0, DSP 1, ... DSP 9), while the unified style requires 30 op-codes (FIX 0, FIX 1, ... FIX 9; SCI 0, ... SCI 9; ENG 0, ... ENG 9), too costly a sacrifice for the HP 67.
As the HP 25 had a not-so-rich instruction set, it could spend more op-code space without too much concern.
The HP 41 introduced multi-byte instructions, so the restriction was avoided.
Of course, op-codes are the manner in which instructions are stored as program steps.