16 Bit CPU

16-Bit CPU made in Logisim

This is fully functional CPU for which you can write your own program in his assembly.

Instructions

1. Zero Adress instructions

   • HALT - 0000 0000 - Shuts down the processor
   • RTS - 0000 0001 - Returns from subroutine
   • RTI - 0000 0010 - Returns from interrupt routine
   • ASL - 0000 0011 - Aritmethic shift left
   • POPPSW - 0000 0100 - Pops PSW from the stack
   • PUSH - 0000 0101 - Pushes Accumulator to the stack
   • POP - 0000 0110 - Pops Accumulator from the stack

2. Branch instructions

   • BEQL - 0001 0000 - Branches to PC+Third byte if PSWZ=1
   • BNEQ - 0001 0001 - Branches to PC+Third byte if PSWZ=0
   • BLEQU - 0001 0010 - Branches to PC+Third byte if ( PSWC + PSWZ )=1
   • BLSS - 0001 0011 - Branches to PC+Third byte if ( PSWN xor PSWV) =1
   • JLEQ - 0001 0100 - Jumps to the address given by the 3rd and 4th instruction byte
   • JMP - 0010 0000 - Jumps to the address given by the 2rd and 3th instruction byte
   • JSR - 0010 0001 - Jumps to the address given by the 2rd and 3th instruction byte

3. Adress instructions

   • LD - 0011 0000 - Loads into the Accumulator
   • ST - 0011 0001 - Stores to the memory location
   • JADR - 0011 0010 - Jumps to the address
   • TST - 0011 0011 - "Logical and" ("&") of the Accumulator and second operand without changing the accumulator value, thus only updating PSW
   • XOR - 0011 0100 - XOR with changing the accumulator
   • STRLEN - 0011 0101 - Measures length of a string, operand is a pointer to the string, 00h is regarded as the end of the string character

Types of addressing

• immed - Operand is given in instruction Bytes
• memdir - Memory location of operand is in instruction Bytes
• regdir - Register which stores the operand is given in instructions Bytes
• memind - Memory location which stores the memory location of operand is given in instructions Bytes
• preincr - Increment of instruction Bytes gives us register which has operand
• postdec - Register which stores the operand is given in instructions Bytes, which are to be decremented after instruction
• regindpom - Memory location of operand = Content of given register + next instruction Byte