\documentclass{book}
\usepackage{tikz}

\title{Unnamed Machine}
\author{A Very Terrible 16-bit Machine}

\begin{document}
	\maketitle
	\tableofcontents
	\chapter{Overview}
	\section{Introduction}
	This is a very poorly thought out 16-bit machine, but you've got to start somewhere. Currently debating between a CPU status register, 80x86 style, or just placing arithmetic results into a predetermined register. This is more of a load–store architecture to try and keep the instruction set simple.
	\section{Registers}
	The following are the general purpose registers that can be used.
	\begin{itemize}
		\item[] R1
		\item[] ...
		\item[] R8
	\end{itemize}
	\section{Memory Model}
	Memory will be implicitly mapped I/O. The bottom 3201 bytes of memory will be reserved for the keyboard input and graphics.
	A single byte is reserved for the keyboard's input. The current key will be stored in byte 0xF37E, with the most significant bit being a flag indicating that the keyboard 
	is ready to be read from. This means that the character encoding is actually 7 bits.
	Video memory starts at 0xF37F (62335 decimal), and every byte represents an ASCII character in monochrome.
	\begin{figure}
		\centering
		\begin{tikzpicture}
			\fill[gray!5] (0,0)rectangle(5,10);
			%\draw (0,10) .. controls (-2,6) and (-2,4) .. (0,1);
			%\draw (0,10) arc (0:180:3cm);
			\draw (0,10) -- (5,10);
			\draw (0,1) --  node[above] {Video 0xF37F} (5,1);
			\draw (0,0) -- (5,0);
			\node[label=right:Top 0x0000] at (5,10) {};
			\node[label=right:Bottom 0xFFFF] at (5,0) {};
		\end{tikzpicture}
		\caption{Memory Layout}
	\end{figure}
	\chapter{Instruction Set Architecture}
	\section{Instruction Encoding}
	Instructions are fixed to exactly one byte (8 bits).
	Instructions that work with two operands the register for operand one will be encoded in the three least significant bits. So an instruction with format XXXX X000 will use Register 1 and so forth all the way to the pattern XXXX X111, which will be Register 8.
	\begin{figure}
		\centering
		\begin{tabular}{ c c }
			\hline
			Instruction & Register \\
			\hline\hline
			0000 0 & 000 \\
			\hline
		\end{tabular}
		\caption{Encoding Layout}
	\end{figure}
	\section{STOB (Store Byte)}
	\begin{tabular}{ c c c c }
		\hline
		Opcode & Mnemonic & Operand 1 & Operand 2 \\
		\hline\hline
		0x20 & stob & Register & Memory Address \\
		\hline
	\end{tabular}\\[6pt]
	Stores a single byte (the lower nibble) from a register to a memory address.
	\section{STOW (Store Machine Word)}
	\begin{tabular}{ c c c c }
		\hline
		Opcode & Mnemonic & Operand 1 & Operand 2 \\
		\hline\hline
		0x20 & stow & Register & Memory Address \\
		\hline
	\end{tabular}\\[6pt]
	Stores a machine word from a register to a memory address.
	\section{LODB (Load Byte)}
	\begin{tabular}{ c c c c }
		\hline
		Opcode & Mnemonic & Operand 1 & Operand 2 \\
		\hline\hline
		0x20 & lodb & Register & Address \\
		\hline
	\end{tabular}\\[6pt]
	Loads a single byte into a register from a memory address.
	\section{LODW (Load Machine Word)}
	\begin{tabular}{ c c c c }
		\hline
		Opcode & Mnemonic & Operand 1 & Operand 2 \\
		\hline\hline
		0x20 & lodw & Register & Address \\
		\hline
	\end{tabular}\\[6pt]
	Loads a word into a register from a memory address.
	\section{CMP (Compare)}
	\begin{tabular}{ c c c c }
		\hline
		Opcode & Mnemonic & Operand 1 & Operand 2 \\
		\hline\hline
		0x80 & cmp & Register & Register \\
		\hline
	\end{tabular}\\[6pt]
	Compares two registers and somewhere sets a result, maybe in register 1?
	\section{ADD (Add)}
		\begin{tabular}{ c c c c }
		\hline
		Opcode & Mnemonic & Operand 1 & Operand 2 \\
		\hline\hline
		0x40 & add & Register & Register \\
		\hline
	\end{tabular}\\[6pt]
	Performs addition on a register with a value from another (or the same) register.
	\section{SUB (Subtract)}
	\begin{tabular}{ c c c c }
		\hline
		Opcode & Mnemonic & Operand 1 & Operand 2 \\
		\hline\hline
		0x60 & sub & Register & Register \\
		\hline
	\end{tabular}\\[6pt]
	Performs subtraction on a register with a value from another (or the same) register.
	\section{JMP (Jump)}
	\begin{tabular}{ c c c c }
		\hline
		Opcode & Mnemonic & Operand 1 & Operand 2 \\
		\hline\hline
		0x60 & jmp & Address & None \\
		\hline
	\end{tabular}
	Jumps unconditionally to a memory address.
	\section{JZ (Jump if Zero)}
	\begin{tabular}{ c c c c }
		\hline
		Opcode & Mnemonic & Operand 1 & Operand 2 \\
		\hline\hline
		0x60 & jz & Address & None \\
		\hline
	\end{tabular}
	Jumps to a memory address if some register is zero.
	\section{JG (Jump if Greater Than)}
	\section{JL (Jump if Less Than)}
	\section{AND (Logical AND)}
	\section{XOR (Logical Exclusive OR)}
	\section{OR (Logical OR)}
	\section{NOT (Logical Negation)}
	\section{SHR (Shift Right)}
	\section{SHL (Shift Left)}
	
\end{document}