On Sun, Nov 20, 2016 at 7:29 PM, Jon Elson <el...@pico-systems.com> wrote: > On 11/20/2016 05:30 PM, Charles Dickman wrote: >> >> On Fri, Nov 18, 2016 at 6:15 PM, Jon Elson <el...@pico-systems.com> wrote: >> >>> OH, yeah! Besides the limited instruction set, short registers only half >>> populated, etc., did you know that the 360/20 did not have an adder? >> >> This made me curious about how primitive it was, but the FE docs on >> bitsavers show a 16bit ALU that can do ADD, AND, OR and XOR and maybe >> some logic to help with BCD math. >> > OK, in this manual : > http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/360/fe/2020/Z26-5908_360-20_FE_Manual_Of_Instruction_Aug65.pdf > > They describe the functions available in microcode. They are REALLY > limited! > See Page 1-23, Description, item 4. They have data transfer and increment > and decrement. > Period! I don't see ANYTHING that relates to ALU functions! Maybe I missed > it, it seems really hard to believe. > > and then page 1-27 describing what the increment and decrement commands do. > Notably, they note that the registers contain values from 0-15, ie. a 4-bit > field. > > Maybe I missed the whole point of what they are describing here, but this > seems to be somewhat consistent with what you can pack into a 16-bit > microinstruction, namely, not a lot. > > Take a look in this manual and see if you get a different impression. > > Jon
I was looking here: http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/360/fe/2020/Z33-1021-0_2020_Processing_Unit_FETOM_May68.pdf (pdf) pages 45, 46 describe the ALU And here: http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/360/fe/2020/SY33-1024-0_2020_FEMDM_Vol_1_Apr69.pdf (pdf) pages 15 and 38 Data flows and ALU schematic
