S80 Retro 1.0

Last updated on 31 October 2018 by Robin & Filip Pynckels   LinkedIn profile Filip Pynckels Facebook page S80 computer GitHub repositories Filip Pynckels



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Introduction

31 October 2018   Welcome to this webpage concerning an expandable Z80 retro computer. Our goal is to make a Z80 based computer with retro technology.

Please note that we publish all information as we put it in writing, which makes that some functionality can still be missing, that some boards are only in production version 1.0, that other boards already are in the design phase of a next version, etc.

Why would you do that, we hear you ask. Well, there are multiple things that come to mind. One of us started his computer experience with a VIC20, in the era where Z80 and 6502 processors were state of the art. We have, since a long time, the wish to construct a computer with comparable technology ourself. And now, the time has come.

A second element is that lately, more and more people are interested in the retro technology we counted to use to make our computer. More and more people wish to understand the nitty gritty details of this technology, and want to play with it. Our initiative permits people to play with the used technology (or to create magic smoke) using a cheap computing environment.

The third goal is to permit people to extend their computing environment with all kinds of extra functionality (think about the internet of things) without having to guess how to integrate it with that environment. Documentation will be as extensive as time permits.

Everything on this site is public domain under the MIT license and can be used to develop or extend the readers projects or ideas. We would concider it an honour if people would take our design and construct other modules for it. And we're ready to give any support possible if they want to do so.

The fact that we put a copyright notice on our documents and deliverables does not mean that we want to protect our ideas. On the contrary, it gives us the possibility to keep this entire biotope under the MIT and the open hardware license, without someone trying to make it poprietary.

We are looking for people who want to extend this open source/hardware platform:

For more detailed examples of the challenges that lay ahead, one can take a look at the issues section of the S80 Github repository. This Github repository contains all the hardware designfiles and software that we have for the moment.

If you have questions, remarks or hints, or if you want to work together with us on the S80, please don't hesitate to contact us. We can be reached on Facebook, LinkedIn or Github.


Architecture

11 August 2018   We have chosen for a classic single bus architecture for our expandable Z80 retro computer. The bus is divided into:

We also provide a secondary bus with 16 user lines to permit later expansion by us or by third parties.

 A top level schematic (in pdf format) of the architecture we have designed can be found by clicking on the below image. The bus components (address, data, control, power, user) are further clarified in this high-level architecture overview.

S80 Retro - Top level architecture

Below, we will document one component at a time. By default, each component will have it's own PCB, except if grouping components seems like a logic decision to save space, or to regroup functionalities so to make using this computer more self explaining.


Design specifications

31 October 2018    Designing is also choosing the right tools to get the right things done in the most efficient way. In this case, the first choice to make was which tool we would use for the design of our schematics and our PCBs. We chose KiCad. It could have been an other tool, and we're certainly not saying that this is the best tool, but hey, it's free, and it's good.

 The design idea is that there will be 6 different board sizes. The boards will be stackable without limit. The boards will form (eventually supported by spacers) kind of a piramid shape. But, since the stacking of the boards is not limited, they can also form a diabolo shape, a cube shape, a beam shape, etc. In fact, it should be elegant if not put in a case, and it should be easy to put it as compact as possible in a case for production purposes.

All components will be through-hole except if the required functionality does not exist in DIP package. But through-hole or not, all components will be at the top side of the boards, in order to guarantee a uniform and elegant view.

Boards created by third parties can have any shape, but it would be nice if they would also concider the default measures and the default side of the board to put their components on.

The printed circuit boards will be made available in 6 colors: green, blue, yellow, red, white and black. All with white silk screens, except the white boards that will have black silk screens.

Finally, the distance between the stackable headers (A, D, C) and (U) and the stackable headers (U0..U7) and (U8..U15) must permit to put a normal breadboard between two layers of the S80 as to be able to do fast temporary tests that are part breadboard and part S80. The vertical distance between any two consecutive layers of the S80 must also permit to put a standard breadboard between them.

To print the design specifications for the 6 boards in real size, click on the below image to get a pdf file with this information.

S80 Retro - Design specifications

 The technical design will be so that it gives new and/or unexperienced users a certain protection against error and magic smoke. One can think about as much copper filled areas (Vcc and Gnd) as possible, buffering of more expensive chips, current-protection, voltage clamping, etc. Each board design must go through a phase of "user friendlyness checking" before it will be released from schematics quality control.

 The PCB design rules we use are:

 A first impression of the stacked boards and of the S80 do it yourself kit can be found by clicking on the below image. Please take into account that only these boards are in the final test stage. The piramid shape will begin to show itself when more and more boards become available.

S80 Retro - Design stacked       S80 Retro - DIY kit

S80 Clock

31 October 2018    Description

This board constitutes the hart of the S80. It is composed of multiple oscillators. The frequencies are chosen so to accomodate most of the retro Z80's that are available on the market today.

The Clock board contains 2x8 jumper pins. It will only contain one jumper. The reason we are working with jumpers, and not with dipswitches and that we only join one jumper with the board is to protect the user against himself. More specific, putting more than one jumper in place would link two or more oscillator outputs together, with an unpredictable voltage, current and wave form as a consequence.

The pins that are jumpered send the signal of the corresponding oscillator to the /CLK (C1) bus. It is, however, possible to use the pins of the other oscillators to break out the oscillator signal to an other board, or to the user bus. This is the reason that we include place for 4 supplementary user oscillators. This permits to concentrate all clock functionality on one board, without substantially limiting the number of available clock signals.


 Technical specifications

Should any further specifications be necessary or useful, please don't hesitate to contact us, so that we can complete the below table.

Author/Creator Robin & Filip Pynckels
License MIT License (open hardware and software)
Remark The clock logic is regrouped with the power and the reset logic on one board.
Status Production boards are ready.
Do it yourself kits are ready.
Looking into means to ship and reimburse.
PCB Manufacturer JlcPcb
(batch numbers: 2396351A-Y4-180909)
Dimensions (W x H x D) 127.0mm (5.0") x 73.7mm (2.9") x 1.6mm (0.063")
Outgoing bus signals C1 (non-buffered)
Incoming bus signals P[0, 1] (no protection build in)
Biderectional bus signals -
User bus signals -
Reserved Memory addresses -
Reserved IO addresses -


 Schematics

A schematic (in pdf format) of the S80 Clock board can be found by clicking on the below image.

S80 Retro - Clock board schematics


 PCB (Printed Circuit Board)

A schematic (in pdf format) and an image of the S80 Clock board's PCB can be found by clicking on the below images.

S80 Retro - Clock board schematics       S80 Retro - Clock board picture


 Populated board

An impression of the populated S80 Clock board is not available.


S80 Memory

31 October 2018    Description

This board constitutes the short- and long-term memory of the S80. It is composed of one or more EEPROM's and two static RAM chips. Together with some logic circuits to interact with the address bus, the data bus and the control bus.

The incoming signals are not clipped nor clamped, so care should be taken not to pass the 5 volt limit. Nor should a current peak occur in one of the busses when this memory board is used.

The Memory board contains 2x8 pins for jumpers. These serve to provide as much RAM as possible, without blocking the number of EEPROM bytes that can be used. More specific, this board permits to use between 0 and 32Kb of EEPROM bytes. The dipswitches permit to set the number of used 128 byte EEPROM segments (starting from address 0x0000). RAM starts immediately after the last EEPROM segment as defined by the dipswitches. It is possible to use no EEPROM bytes. In this case, all dipswitches must be set to 0.

An other 2x3 male header permits to choose between one of three EEPROM's.


 Technical specifications

Should any further specifications be necessary or useful, please don't hesitate to contact us, so that we can complete the below table.

Author/Creator Robin & Filip Pynckels
License MIT License (open hardware and software)
Status Production boards are ready.
Do it yourself kits are ready.
Looking into means to ship and reimburse.
PCB Manufacturer JlcPcb
(batch numbers: 2396351A-Y5-180909)
Dimensions (W x H x D) 152.4mm (6.0") x 73.7mm (2.9") x 1.6mm (0.063")
Outgoing bus signals -
Incoming bus signals A[0..15] (non-clamped, accepts high impedance mode if C[8, 9, 10] are not floating)
C[8, 9, 10] (non-clamped, does not accept high impedance mode)
P[0, 1] (no protection build in)
Biderectional bus signals D[0..7] (non-buffered, non-clamped, can go in high impedance mode,
accepts high impedance mode if C[8, 9, 10] are not floating)
User bus signals -
Reserved Memory addresses 0x0000 :: 0xFFFF
Reserved IO addresses -


 Schematics

A schematic (in pdf format) of the S80 Memory board can be found by clicking on the below image.

S80 Retro - Memory board schematics


 PCB (Printed Circuit Board)

A schematic (in pdf format) and an image of the S80 Memory board's PCB can be found by clicking on the below images.

S80 Retro - Memory board schematics       S80 Retro - Memory board picture


 Populated board

An impression of the populated S80 Memory board is not available.


S80 Power

31 October 2018    Description

This board constitutes the energy plant of the S80. It is composed of a simple circuit that regroups the power signals (5V and GND) and the serial IO signals. The reason is that we have opted to use, for the first version, an USB to serial TTL cable that converts the USB protocol for us. A later version will contain a USB to serial TTL circuit on-board.

The only other element that is available in the power circuit is a power smoothing capacitor and a clipping Zener diode of 5v1.


 Technical specifications

Should any further specifications be necessary or useful, please don't hesitate to contact us, so that we can complete the below table.

Author/Creator Robin & Filip Pynckels
License MIT License (open hardware and software)
Remark The power logic is regrouped with the clock and the reset logic on one board.
Status Production boards are ready.
Do it yourself kits are ready.
Looking into means to ship and reimburse.
PCB Manufacturer JlcPcb
(batch numbers: 2396351A-Y4-180909)
Dimensions (W x H x D) 127.0mm (5.0") x 73.7mm (2.9") x 1.6mm (0.063")
Outgoing bus signals -
Incoming bus signals -
Biderectional bus signals -
User bus signals U1 (non-buffered, outgoing on bus and incoming on connector, Rx)
U2 (non-buffered, incoming on bus and outgoing on connector, Tx)
Reserved Memory addresses -
Reserved IO addresses -


 Schematics

A schematic (in pdf format) of the S80 Power board can be found by clicking on the below image.

S80 Retro - Power board schematics


 PCB (Printed Circuit Board)

A schematic (in pdf format) and an image of the S80 Clock-Power-Reset board's PCB can be found by clicking on the below images.

S80 Retro - Power board schematics       S80 Retro - Power board picture


 Populated board

An impression of the populated S80 Power board is not available.


S80 Processor

31 October 2018    Description

This board constitutes the brains of the S80. It is composed of the Z80 CPU, together with some logic circuits to interact with the address bus, the data bus and the control bus.

The incoming signals are clipped between Vcc and Gnd. They have pull-up to Vcc and have current protection against mild overloading peeks.


 Technical specifications

Should any further specifications be necessary or useful, please don't hesitate to contact us, so that we can complete the below table.

Author/Creator Robin & Filip Pynckels
License MIT License (open hardware and software)
Status Production boards are ready.
Do it yourself kits are ready.
Looking into means to ship and reimburse.
PCB Manufacturer JlcPcb
(batch numbers: 2396351A-Y3-1800809)
Dimensions (W x H x D) 101.6mm (3.0") x 73.7mm (2.9") x 1.6mm (0.063")
Outgoing bus signals A[0..15] (buffered, can go in high impedance)
C[4, 7..11] (buffered, can go in high impedance)
C5, C13 (non-buffered, no high-impedance mode)
Incoming bus signals C[0..3, 6, 12] (clamped, accept high impedance mode)
P[0, 1] (no protection build in)
Biderectional bus signals D[0..7] (buffered)
User bus signals -
Reserved Memory addresses -
Reserved IO addresses -


 Schematics

A schematic (in pdf format) of the S80 Processor board can be found by clicking on the below image.

S80 Retro - Processor board schematics


 PCB (Printed Circuit Board)

The printed circuit board has been tested and verified under a microscope. A schematic (in pdf format) and an image of the S80 Processor board's PCB can be found by clicking on the below images.

S80 Retro - Processor board schematics       S80 Retro - Processor board picture


 Populated board

An impression of the populated S80 Processor board can be found by clicking on the below image.

S80 Retro - Processor populated board picture


 More pictures

We have done substantial testing and we are confident that the processor board is ready for distribution.

S80 Retro - Processor test 1 picture       S80 Retro - Processor test 2 picture

S80 Reset

31 October 2018    Description

This board contains the reset switch for the entire configuration.

This reset is a normal reset as generally known and used (we provide 10ms of pulse so to give the processor at least 3 processor cycles as required in the technical specs of the Z80).

The power on reset (delayed reset when the hardware is powered on in order to let all IC's start up before the Z80) is included in the left part of the normal reset circuit.

The reset as described in the US patent 4486827 is a bit peculiar, and is not implemented for the moment. The next version of the reset circuit will probably contain this reset logic.

In short: this button resets only during the first two cycles (T1 and T2) of the operation, characterised by /M1 being low. The goal of this reset is to use the same /RESET control input to the processor as a normal reset, to reset only the program counter to facilitate development (breakpoints)."


 Technical specifications

Should any further specifications be necessary or useful, please don't hesitate to contact us, so that we can complete the below table.

Author/Creator Robin & Filip Pynckels
License MIT License (open hardware and software)
Remark The reset logic is regrouped with the clock and the power logic on one board.
Status Production boards are ready.
Do it yourself kits are ready.
Looking into means to ship and reimburse.
PCB Manufacturer JlcPcb
(batch numbers: 2396351A-Y4-180909)
Dimensions (W x H x D) 127.0mm (5.0") x 73.7mm (2.9") x 1.6mm (0.063")
Outgoing bus signals C0 (non-buffered, no high-impedance mode)
Incoming bus signals C[1, 4] (no protection build in)
P[0, 1] (no protection build in)
Biderectional bus signals -
User bus signals -
Reserved Memory addresses -
Reserved IO addresses -


 Schematics

A schematic (in pdf format) of the S80 Reset board can be found by clicking on the below image.

S80 Retro - Reset board schematics


 PCB (Printed Circuit Board)

A schematic (in pdf format) and an image of the S80 Clock-Power-Reset board's PCB can be found by clicking on the below images.

S80 Retro - Reset board schematics       S80 Retro - Clock board picture


 Populated board

An impression of the populated S80 Clock-Power-Reset board is not available.


 More pictures

The reset circuit resets on demand, and does a delayed reset on power on (see below graphics). It should provide the special debugging reset, but that feature is not implemented yet.

S80 Retro - Reset - Power On - Falling edge picture       S80 Retro - Reset - Power On - Rising edge picture

S80 Serial

31 October 2018    Description

This board constitutes the sences of the S80. It is composed of a, 16C550 UART chip, together with some logic circuits to interact with the address bus, the data bus and the control bus.

The incoming low address byte is compared with an address set by jumpers. It should be equal. It is advised to set the address with the jumpers to 0xC0. This will use the IO address range 0xC0 to 0xC7. An other address can be used, although care should be taken not to interfere with the IO addresses of other boards.


 Technical specifications

Should any further specifications be necessary or useful, please don't hesitate to contact us, so that we can complete the below table.

Author/Creator Robin & Filip Pynckels
License MIT License (open hardware and software)
Status Production boards are ready.
Do it yourself kits are ready.
Looking into means to ship and reimburse.
PCB Manufacturer JlcPcb
(batch numbers: 2396351A-Y6-180909)
Dimensions (W x H x D) 127.0mm (4.0") x 73.7mm (2.9") x 1.6mm (0.063")
Outgoing bus signals C3 P[0, 1] (outgoing on TTL conn pins 2 and 1)
Incoming bus signals A[0..7] (checked on address range set by dipswitches)
C0, C4, C8, C9, C11 (no protection build in)
P[0, 1] (no protection build in)
Biderectional bus signals D[0..7] (no protection build in)
User bus signals U[1, 2] (outgoing on U-bus & TTL conn pins 3 and 4)
Reserved Memory addresses -
Reserved IO addresses Variable base address in multiples of 0x08. Advised addresses are 0xC0 (base address) :: 0xC7


 Schematics

A schematic (in pdf format) of the S80 Serial board can be found by clicking on the below image.

S80 Retro - Serial board schematics


 PCB (Printed Circuit Board)

A schematic (in pdf format) and an image of the S80 Serial board's PCB can be found by clicking on the below images.

S80 Retro - Serial board schematics       S80 Retro - Clock board picture


 Populated board

An impression of the populated S80 Serial board is not available.


 More pictures

This serial board permits to communicate between the S80 and a serial terminal emulation program. Initial tests are simplistic, but conclusive.

S80 Retro - Processor test 1 picture

S80 Breakout 2"

31 October 2018    Description

This board is the top plate of the S80 computer configuration. At the same time, it is the smallest board that gives the user the possibility to append little things to the S80, since all busses are broken out on this board, without any further protection or precautions. This gives the user full control over the entire S80 configuration and all its busses, memory addresses, IO addresses, etc. Care has been taken that even a 40-pin DIP socket can be places on this board, together with some small components.

This board is not suited for wire-wrapping. The diameter of the pads is only 0.8mm (0.031") which makes them not suited for wire-wrapping sockets, but more snug for through hole components.


 Technical specifications

Should any further specifications be necessary or useful, please don't hesitate to contact us, so that we can complete the below table.

Author/Creator Robin & Filip Pynckels
License MIT License (open hardware and software)
Status Production boards are ready.
Do it yourself kits are ready.
Looking into means to ship and reimburse.
PCB Manufacturer JlcPcb
(batch numbers: 2396351A-Y2-180724)
Dimensions (W x H x D) 53.3mm (2.1") x 73.7mm (2.9") x 1.6mm (0.063")
Outgoing bus signals -
Incoming bus signals -
Biderectional bus signals A[0..15] (no protection build in)
D[0..7] (no protection build in)
C[0..13] (no protection build in)
P[0, 1] (no protection build in)
User bus signals U[0..15] (no protection build in)
Reserved Memory addresses -
Reserved IO addresses -


 Schematics

A schematic (in pdf format) of the S80 2inch breakout board can be found by clicking on the below image.

S80 Retro - 2inch breakout board schematics


 PCB (Printed Circuit Board)

The printed circuit board has been tested and verified under a microscope. A schematic (in pdf format) and an image of the S80 breakout board's PCB can be found by clicking on the below images.

S80 Retro - 2inch breakout board schematics       S80 Retro - 2inch pcb picture


 Populated board

An impression of the populated S80 2inch breakout board can be found by clicking on the below image.

S80 Retro - 2inch populated pcb picture


 More pictures

This breakout board is ready for distribution. Please note that the components (resistors, capacitors, switch, 555 timer and socket, testpins) are not delivered with this board.

On demand, the testpins can be delivered with the board in the different board colors (black, blue, green, red, white, yellow). These testpins are a substantial added value when probing and/or using a protocol analyser.

S80 Retro - Processor test 1 picture       S80 Retro - Processor test 2 picture

S80 Breakout 7"

31 October 2018    Description

This board is the base plate of the S80 computer configuration. At the same time, it is the board that gives the user the possibility to experiment with the S80, since all busses are broken out on this board, without any further protection or precautions. This gives the user full control over the entire S80 configuration and all its busses, memory addresses, IO addresses, etc.

This board is not suited for wire-wrapping. The diameter of the pads is only 0.8mm (0.031") which makes them not suited for wire-wrapping sockets, but more sturdy for through hole components.


 Technical specifications

Should any further specifications be necessary or useful, please don't hesitate to contact us, so that we can complete the below table.

Author/Creator Robin & Filip Pynckels
License MIT License (open hardware and software)
Status Production boards are ready.
Do it yourself kits are ready.
Looking into means to ship and reimburse.
PCB Manufacturer JlcPcb
(batch numbers: 2396351A-Y1-180724)
Dimensions (W x H x D) 177.8mm (7.0") x 73.7mm (2.9") x 1.6mm (0.063")
Outgoing bus signals -
Incoming bus signals -
Biderectional bus signals A[0..15] (no protection build in)
D[0..7] (no protection build in)
C[0..13] (no protection build in)
P[0, 1] (no protection build in)
User bus signals U[0..15] (no protection build in)
Reserved Memory addresses -
Reserved IO addresses -


 Schematics

A schematic (in pdf format) of the S80 7inch breakout board can be found by clicking on the below image.

S80 Retro - 7inch breakout board schematics


 PCB (Printed Circuit Board)

The printed circuit board has been tested and verified under a microscope. A schematic (in pdf format) and an image of the S80 breakout board's PCB can be found by clicking on the below imagese.

S80 Retro - 7inch breakout board schematics       S80 Retro - 7inch pcb picture


 Populated board

An impression of the populated S80 7inch breakout board can be found by clicking on the below image.

S80 Retro - 7inch pcb picture


 More pictures

This breakout board permits to make through-hole circuits but also permits to fit a breadboard between two layers of the S80 so to make circuits to test whatever inspiration you have within minutes and without soldering. On demand, a breakout board that permits wire-wrapping can be provided.

S80 Retro - Processor test 1 picture       S80 Retro - Processor test 1 picture

Third party extensions

31 October 2018    Introduction

The entire concept of this S80 expandable retro computer is that extensions can be created, and software can be developped at will by everyone who is interested. It goes without saying that nobody is forced to document his or her extensions.

However, we are convinced that it is more productive, and hence more fun for everyone if there is some documentation regarding the extension you have created.

Therefore, we'd like to ask that, when you create an extension, you also take the time to provide at least the information that can be useful for others to use and maybe build further on your concept.

A great place to discuss actual and future hardware and software is the S80 Github repository. And especially the issues section of the Github repository.

We are ready, when you create an extension, and a webpage with documentation, to publish a link to your webpage. If you don't want to create a webpage but make your extension known to the broader public anyway, then we are ready to mention your extension on this page, using the structure (see above) we use for our own boards (including the name of the author/creator and the license under which you want to make your work available)..

We hope that, this way, our idea and your extensions can grow into an interesting and fun total concept.


Manufacturing

11 August 2018    Manufacturing good PCBs for a reasonable price. The question was who to find to help us. Our requirements were:

 The design rules we use (and that have to be supported) are:

 To choose a manufacturer we ordered a number of PCB's at different manufacturers, and most of them had their pros and cons. Again, they are undoubtedly not the only ones, but for us, the kind and fast reply on questions made us chose for:

JlcPcb

They were the manufacturer that performed by far the best of the many we've tried. Their website offers the possibility to order, pay and follow up our commands without a lot of fiddling at the margins or frustrations.