/diy/ - Do It Yourself

>>2039027
what technology are you designing in? discrete TTL? discrete 4000 series CMOS? CPLD? FPGA? discrete NMOS?
>Any similar *well-documented* and simple chips to draw inspiration from?
these were used in some early MCU-based calculators http://bitsavers.informatik.uni-stuttgart.de/components/ti/TMS1000/TMS1000pgmRef_1975.pdf
these were used in things like microwave ovens and timers http://datasheets.chipdb.org/National/COP400/NS_COP400_Family.pdf
>How many registers do I use?
maybe none, maybe just one accumulator/working register and a condition code register
>How long to make the instructions (8-bit?)?
8-bit is a good size, there's room for a lot of of instructions with 4-bit immediate operands, but you might have to leave yourself room to do some tricks and you'll probably be bank-switching. also remember to deal with long jumps in your instruction encoding, including any skip instructions you might implement
>How many nibbles of RAM is enough for a basic 10-digit calculator?
far less than you can buy as a packaged component tod- oh, Jameco has those 74S189 fuckers NOS for $4 each. anyway. 64 nybbles would be ample, even extravagant. room enough for the display, a memory, a scratchpad, and to memory-map the keyboard
>How deep to make the function stack?
depends on how you structure your code and how big your program store is. 4 levels might be enough, 8 is more than enough. you'll find out for sure when you write the program

>>2039039
in amps don't have external feedback in usual configurations. they just figure the difference between the two inputs, gain it up by an application-specific but controlled multiple, and offset that by a reference input (picrel at R6). not the same thing as op amps
anyway op amps are a low impedance signal source because their output currents are relatively high and R=E/I