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+#+TITLE: Z80
+#+DATE: <2021-03-03>
+#+SETUPFILE: ../../options.org
+
+{{{date_place(Bremen, Germany)}}}
+
+This section is dedicated sharing all the Z80 related work. This
+includes software, schematics and tools that I've designed to
+accomplish this task. It also includes a kind of narration of the
+project itself, throughout its development and changes.
+
+** Articles about the history of the project
+- [[local:/z80/plm.html][PLM: Pocket Lisp Computer]]
+- [[local:/z80/prototype1.html][Prototype 1]]
+- [[local:/z80/prototype2.html][Prototype 2]]
+
+** More technical articles
+- [[local:/z80/spi.html][SPI for microprocessors]]
+
+** External Links
+- [[http://www.z80.info/index.htm][z80.info]] useful z80 resources
+- [[https://www.zilog.com/index.php][Zilog website]]
diff --git a/src/z80/plm.org b/src/z80/plm.org
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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.
diff --git a/src/z80/prototype1.org b/src/z80/prototype1.org
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+#+TITLE: Prototype 1
+#+DATE: <2019-03-03>
+#+SETUPFILE: ../../options.org
+
+#+BEGIN_COMMENT
+m4_define(`_REL_HEADER', `Previous: <a href="/z80/plm.html">PLM</a>
+Next: <a href="/z80/prototype2.html">Prototype 2</a>Up: <a
+href="/z80/">Z80</a>')m4_dnl
+#+END_COMMENT
+
+{{{date_place(Temuco, Chile)}}}@@html:<br>@@ Last edited: Bremen,
+Germany, February 02, 2021
+
+* Background
+
+Back in 2015 I used to watch gameplays of the just released [[https://en.wikipedia.org/wiki/Fallout_4][Fallout 4]].
+From this game the thing I loved the most was the pip-boy, so much so,
+that I had the brilliant idea, /Why don't I build my own pip-boy? I
+mean, How hard could it be?/.
+
+Unsurprisingly, it turned to be harder than expected. I only knew how
+to program at an application level (I wasn't that good at it either)
+and had basically no knowledge of electronics, assembly language, nor
+did I even have the components at my disposal.
+
+* Beginning
+
+Some time after this idea, I got myself an atmel328p and a programmer.
+I learned to instruct this AVR to draw text on a 16x4 lcd and could
+get input from buttons.
+
+But I had some challenges. First, microcontrollers are usually based
+on the Harvard architecture. This means that running programs from ram
+was virtually impossible.
+
+Added to this was the fact that the AVR had only 2K of ram and no way
+to add more. I avoided serial alternatives, because they are slower
+and can't be used as normal RAM inside C code.
+
+These problems were ultimately fixed by switching to a Z80
+microprocessor. The Z80 could in fact handle more memory and run code
+from its RAM, but with it came also the limitation of size. All memory
+had to be external to the chip's package and the processor itself came
+with no peripherals, as microcontrollers usually do.
+
+* First prototype
+
+Three years later, and with the help of many people, I finally
+managed to get all the components and build my first working
+prototype. It did not look beautiful, but it was functional.
+
+#+CAPTION: Prototype 1 together with its serial terminal
+[[https://thomaslabs.org/media/prototype1.jpg]]
+
+I wasn't satisfied with this prototype though. It was not what I had
+envisioned. I wanted to have a pocket computer and this was nothing
+like that. It was huge and full of parts.
+
+* Partial conclusion
+
+Thanks to this project I learned a lot about electronics, programming,
+circuit design and the inner workigs from a computer.
+
+Reinventing the wheel wouldn't have been the only way to acquire this
+knowledge.  But I would definitely recommend it to anyone wanting to
+learn about the internals of computers.
+
+This being said, I can't deny that I still have a lot left to learn.
+
+* The end?
+I wouldn't publish something on the Internet just to say I wasn't able
+to accomplish my dream. Or would I?
+
+It turned out that the idea managed to stay alive long enough, to see
+the day in which I decided to give it another try. This time, hoping
+that the collected knowledge allows me to get further.
+
+This requires its own [[local:/z80/plm.html][series of articles]] though.
diff --git a/src/z80/prototype2.org b/src/z80/prototype2.org
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+#+TITLE: Prototype 2
+#+DATE: <2021-03-03>
+#+SETUPFILE: ../../options.org
+
+#+BEGIN_COMMENT
+m4_define(`_REL_HEADER', `Next: <ahref="/z80/prototype1.html">Prototype 1</a> Up: <a href="/z80/">Z80</a>')m4_dnl
+#+END_COMMENT
+
+{{{date_place(Bremen, Germany)}}}
+
+#+CAPTION: Prototype 2
+[[https://thomaslabs.org/media/prototype2_1.jpg]]
+
+Because when moving to Bremen, I wasn't able to take my old Prototype
+with me, I had to build a new one. This time though, I needed
+something easily modifiable.
+
+
+One of the disadvantages of my first Prototype, was the fact, that it
+took me around 3 days to build and, because it was soldered, it was
+difficult to modify. This made experimenting with new ideas somewhat
+impractical.
+
+Prototype 2 would be a prototyping tool, as such, it had to be built
+with a technique, that allowed for the electrical stability of a
+soldered circuit, but with the flexibility of a breadboard.
+
+This time I chose the wire wrap assembly technique, as it met all
+requirements.
+
+The following is a list of what I was able to accomplish thanks to
+Prototype 2
+
+- New memory banking system that would allow it to handle up to 4 MiB
+  of memory, instead of the default maximum of 64KiB.
+
+- Add a RTC
+
+- Add video capabilities using a 480x320 18-bit color display
+
+- Dual serial ports with complete modem control lines
+
+#+CAPTION: Prototype 2 together with screen
+[[https://thomaslabs.org/media/prototype2_2.jpg]]
+
+It didn't take long until Prototype 2 became incapable of fulfilling
+its task. Once it was clear, which parts would definitely be part of
+the final design, the flexibility of wire wrapping was no longer
+needed. Added to this, the circuit experimented detrimental voltage
+drops, due to the length of wire used. It was now time to design a
+third prototype, this time using a PCB.
diff --git a/src/z80/spi.org b/src/z80/spi.org
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+#+TITLE:  SPI for microprocessors
+#+SETUPFILE: ../../options.org
+
+Bremen, Germany, {{{date}}}
+
+SPI is a useful serial communications interface. It is used in
+hobbyist projects to control from memory ICs to LCD screens and it's
+even possible to read SD cards through it.
+
+Most modern microcontrollers are equiped with built-in SPI support,
+which can be easily used from code without much hardware required. But
+what happends when one wants to interface SPI peripherals with old
+microprocessors? These usually don't have any built-in peripherals and
+, as far as I am aware, there are no enternal peripherals one can buy.
+
+This article aims to provide an overview of how SPI works, the
+instructions on how to build a SPI module for old microprocessors like
+the Z80 and the explanation of how such a module operates.
+
+This is also a part of my ongoing series on the progress of my [[local:/z80][Z80
+based project]].
+
+** Table of Contents
+1) [[#how-does-spi-work][How does SPI work]]
+
+#+NAME: how-does-spi-work
+** 1. How does SPI work
+:PROPERTIES:
+:CUSTOM_ID: how-does-spi-work
+:END: