144 lines
3.5 KiB
Markdown
144 lines
3.5 KiB
Markdown
# ISA V0.7
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# Terms
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The form of this document is a list of instructions set into categories.
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Each instruction starts with the recommended mnemonic and then the parameters for the instruction.
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```
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<Code> <mnemonic> <parameter 1> <parameter 2> ...
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```
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Each parameter is is abbreviated into a category
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- R: Register
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- M: Memory address
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- C: Constant
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Parts of this document marked with **!!** are uncertain and will likely change
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# Instructions
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## Memory & Register Management
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**COPY** _from_, _to_ - Copies the byte in _from_ to the destination _to_\
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0x10 COPY R M\
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0x11 COPY M R\
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0x12 COPY M M\
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0x13 COPY R R
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**ZERO** _to_ - Sets the value in _to_ to 0\
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0x17 ZERO R\
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0x18 ZERO M
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0x19 **SET** R C - Sets the value in R to C
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0x1F **SETB** R - Sets the current memory bank to the value in R
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## Control Flow
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0x00 **NOP** - Does nothing
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**GOTO** _address_ - Moves instruction counter to _address_\
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0x20 GOTO R\
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0x21 GOTO C
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**GOTRUE** R, _address_ - Moves instruction counter to _address_ if R is true\
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0x22 GOTOTRUE R R\
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0x23 GOTOTRUE R C
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0x2A **GOCRY** _address_ - Moves the instruction counter to _address_ if the cary flag is set
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0x2D **CALL** R - Moves the instruction counter to R and pushes the address of the call instruction
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0x2E **RET** - Pops the address of the last call instruction off of the call stack and moves the instruction counter past it.
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0x2F **HCF** - Halt and catch fire.
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## Comparison
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**EQU** _result_, _p1_, _p2_ - Sets _result_ to true if the values in _p1_ and _p2_ are the same\
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0x30 EQU R R R\
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0x31 EQU R R C
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**LT** _result_, _p1_, _p2_ - Sets _result_ to true if the value in _p1_ is less than the value in _p2_\
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0x32 LT R R R \
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0x33 LT R R C
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**GT** _result_, _p1_, _p2_ - Sets _result_ to true if the value in _p1_ is greater than the value in _p2_\
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0x34 GT R R R \
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0x35 GT R R C
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Reserved for LEQ GEQ
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0x36\
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0x37\
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0x38\
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0x39
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## Logic / Bitwise
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**OR** R, _value_ - Sets each bit in R to its OR with the respective bit in _value_\
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0x40 OR R R\
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0x41 OR R C
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**AND** R, _value_ - Sets each bit in R to its AND with the respective bit in _value_\
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0x42 AND R R\
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0x43 AND R C
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**XOR** R, _value_ - Sets each bit in R to its XOR with the respective bit in _value_\
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0x44 XOR R R\
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0x45 XOR R C
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**LBS** R, _quantity_ - Shifts each bit in R to the left by _quantity_. Fills new bits with 0\
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0x46 LBS R R\
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0x47 LBS R C
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**RBS** R, _quantity_ - Shifts each bit in R to the right by _quantity_. Fills new bits with 0\
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0x48 RBS R R\
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0x49 RBS R C
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0x4A **NOT** R - Flips each bit in value R
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## Arithmetic
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**ADD** _to_, _from_ - Adds to the the byte in _to_ with the value in _from_\
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0x50 ADD R R\
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0x51 ADD R C
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**SUB** _to_, _from_ - Subtracts from the value in _to_ by the value in _from_\
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0x52 SUB R R\
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0x53 SUB R C
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0x5E **INC** R - Increments the value in R by 1
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0x5F **DEC** R - Decrements the value in R by 1
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## IO
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!! **INTXT** R - Read 1 byte of input to R
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0xF0 **OUTXT** R - Prints the value in R to output as ASCII
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0xF1 **OUT** R - Prints the value in R to output as base 10
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0xFF **VRB** R - Selects the bank number in R to be used as VRAM
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# What is True?
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True is defined as having the least significant bit in a byte set to 1. False is defined as having the least significant bit in a byte set to 0.
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# What are flags
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The CPU has the following flags
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- Carry
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Flags are set as the result of instructions.
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## Carry
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When the add instruction runs, the result can be greater than 8 bits in size. In this case, the carry flag is set true.
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!! The cary flag is set to false in two cases: At the start of an **ADD** instruction, and after running a **GOCRY** instruction
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