3 ms·
Yes, and that was exactly my point (yes, I wrote that SO answer). The indirect addressing mode that were introduced with 68020 are insane. Most people don't kno
by gallier2 3y ago
Yes, and that was exactly my point (yes, I wrote that SO answer). The indirect addressing mode that were introduced with 68020 are insane. Most people don't know them, as they didn't exist in 68000/68010/68008 and most compilers did not implement them as they were slower to use than using simpler composed addressings.
It is interesting to see what Motorola cut from the instruction set when they defined the Coldfire subset (for those who don't know, the coldfire family of CPU used the same instruction set as 68000 but radically simplified, the indirect addressing methods, the BCD mode, a lot of RMW instructions, etc. were removed. The first coldfire after 68060 which was limited to 75Mhz, ran at up to 300MHz).
- mst 3y agoThis makes me wonder if there's any record of why Motorola thought that feature was worth implementing in the first place.
- lstodd 3y agoWell I always wondered why 6502 had BCD. What was the point? I guess it was sorta fashionable back then.
- hulitu 3y agoMaybe to drive LED alphanumeric display segments.
- wiml 3y agoBCD modes only take a few gates to implement; their biggest cost is probably the instruction encoding space they occupy. On a chip as small as the 6502 it makes sense that some users would want to avoid the expensive decimal/binary conversions and do arithmetic in decimal.