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+#+TITLE: PLM
+#+SUBTITLE: The Pocket Lisp Machine (except its not)
+#+DATE: <2021-03-03>
+#+SETUPFILE: ../../options.org
+
+#+BEGIN_COMMENT
+m4_define(`_REL_HEADER', `Next: <a href="/z80/prototype1.html">Prototype 1</a>Up: <a href="/z80/">Z80</a>')m4_dnl
+#+END_COMMENT
+
+{{{date_place(Bremen, Germany)}}}
+
+* Background
+
+If you have read my article about my first [[local:/z80/prototype1.html][Z80 prototype]], then you
+probably already know, what all of this is about. But, as a small
+recap, the idea of my project is to build a pocket computer that can
+be carried around like the pip-boy from the [[https://en.wikipedia.org/wiki/Fallout_(series)][Fallout]] series.
+
+The exact objectives have changed with the development of the computer
+itself. I soon realized, that the way a user would interacts with a
+pip-boy, was less than optimal. A keyboard was mandatory. I also
+changed my mind about what processor I should use for the project,
+starting with an AVR and later with a Z80.
+
+
+As of right now, the objectives are the following:
+
+* Objectives
+
+- Have a pocket computer, that can be carried like a wrist watch
+
+- It should have as much RAM as its possible with a 8-bit CPU
+
+- It will run a lisp interpreter as its operating system
+
+- It would probably end up being used as a scientific calculator
+
+- It has to be expandable enough, so that I can be used as a pocket
+  Arduino replacement
+
+* Pocket Lisp Machine?
+A lisp machine is a computer design to run lisp code. This means, it
+is optimized to do so, be that through special hardware or ISA.
+
+Under this definition, my computer is no lisp machine. But the name
+refers to the fact that it designed to run a lisp interpreter, scheme
+specifically, as its operating system.
+
+
+* Why don't I use a 6502/65816 instead of a Z80?
+Between a Z80 and a 6502 I definitely prefer the Z80. Mainly because
+of the instruction set and peripherals available.
+
+A 65816 would be easier to program than a Z80 due to the built-in
+support for memory banking. But again, I still prefer the peripherals
+of the Z80.
+
+The Z80 DMA is also a important factor for my decision. While it could
+be used with other processors, I prefer to use it together with the Z80.
+
+The last reason is that, I began building my computer using a Z80 and
+would like to complete this project using the same CPU I started with.
+
+
+I do have the idea of building another computer in the future. This
+time based on a WDC 85C816.