artemisamsx / artemisa

Schematics, PCB designs and HDL simulations to build a 8-bits MSX computer

Artemisa MSX Computer System

This repository contains documentation and designs for a MSX computer that can be build using discrete components and original integrated circuits, codenamed Artemisa.

This is still work in progress, but you may find some specs and designs in this repository.

Documentation

• Artemisa User Manual.
• Artemisa Service Manual.

artemisa's Issues

Replace VDP circuit by connection to the external GFX card

Complete the cassette signals circuit

We need the DIN input connector and the different signals connected and processed.

[GFX9918] Fix RCA connectors

Two major issues of RCA connectors:

• The fingerprint does not match. Even though is possible to solder them, the holes are not in the exact position. Also the holes to fit the capsule are missing.
• The poles are inverted. GND is the central pad, while signal is connected to the left and right ones.

Decoupling capacitors of GFX9918 are wrongly valued

Since C5 to C9 use a different nomenclature, the BOM interprets they are different from C3 and C4.

Trace the motherboard PCB

Complete rename of the project

The original idea was to name the project ArteMSX, pronounced "artemis". But I'm afraid this is too tricky and most people would say "arte M-S-X", which is a really terrible name.

The repository has been renamed to apoloval/artemisa. We have to rename the rest of code and documentation to reflect the new name.

Simulate: CPU data bus DIR

Circuit:

3D models of some footprints are not seen in fresh KiCAD installations

Rearrange cassette IO circuit to clarify voltage dividers intention

Place a power LED in the motherboard

Add mounting holes to the motherboard PCB

Document how keyboard works

The PS2 keyboard connected to a microcontroller that simulates the keyboard matrix.

Align GFX bus extension connector to match GFX9918

Complete the PCB layout (footprint positioning) for the motherboard

Using a 25x15cm layout.

Define the interface for a ArteMSX graphics card

The new approach of the project is to consider the graphic card as a separated board. We have to define the interface between the motherboard and the graphics card.

PPI address inputs are wrong

We are passing A14 and A15 to A0 and A1 pins of PPI. That's wrong. They should be A0 and A1.

Test cassette output signal processing

From this schematic:

• Ensure voltage levels of a typical MSX cassette output are in the expected range (52.68mV peak-to-peak according to simulations).
• Ensure a squared signals from the oscilloscope generator is rightly generated.
• Check how that output signal interfaces a real data recorder.

Move clock generation into its own schematic sheet

Test: cassette input signal

Mount the following schematic in a protoboard and test whether expected digital signal is successfully detected using a logic analyzer.

Include a turbo button to increase CPU speed from 3.58Mhz to max supported speed

Here we have a interesting tutorial to have a clock signal selector without glitches build with flip-flops.

Define a expansion bus connector for the libraries

To be used in #12.

Move reset signal generation into its own schematic sheet

Move logic decoding into its own schematic sheet

Document cassette IO

Describe and explain schematics.

Test PSG integration and operation

Things to be tested:

• Decoding logic of the circuit works as expected.
• Clock generation works as expected
• PSG sound works as expected
• Levels of output signal are appropriate

Generate a procedure to burn a ROM image in the flash memory

Add sound connectors to the GFX-9918

Graphics adapters in MSX work are typically connected to TV, via S-VIDEO or SCART connectors. It's also typical to accompany video signals with audio signals to be reproduced in the TV.

Thus, the most suitable movement is to consider the SOUND signal of the GFX expansion slot has the opposite direction as usual. The signal have to go from motherboard to the external card. And the external card has to provide the connections to reproduce the sounds in the external devices.

This task comprises the changes in the GFX-9918 in order to take the sound input from the motherboard and pass it out to RCA connectors.

Move sound line to the graphics card

Graphics adapters in MSX work are typically connected to TV, via S-VIDEO or SCART connectors. It's also typical to accompany video signals with audio signals to be reproduced in the TV.

Thus, the most suitable movement is to consider the SOUND signal of the GFX expansion slot has the opposite direction as usual. The signal have to go from motherboard to the external card. And the external card has to provide the connections to reproduce the sounds in the external devices.

This task comprises the changes in the GFX expansion slot specs, the changes in the symbol, and the corresponding connections in the motherboard to move the sounds output from the PSG to the GFX card.

Order prototype PCBs for GFX9918 Rev1

It's time for rock!

BOM:

• 1x TMS9918
• 1x HM62256ALP-10
• 1x 74HCT04
• 3x 74HCT574
• 1x 74HC32
• 1x Crystal 10.7386Mhz
• 2x Disc capacitor 27pF
• 7x Disc capacitor 100nF
• 1x Radial capacitor 10uF
• 1x Axial resistor 470
• 1x Socket DIP 40 600"
• 1x Socket DIP 28 600
• 1x RCA yellow
• 1x RCA white
• 1x RCA red
• 1x IDC 50p PCB connector male
• 2x IDC 50p ribbon cable female connector
• 1x IDC 50p ribbon cable 5cm

Provide a footprint for the crystals

Test prototype PCBs for GFX9918 Rev1

After #44, it's time to test.

Design the AGFX-9918 graphics card

After graphics card interface is defined by #11, we will design the codenamed AGFX-9918 graphics card, that incorporates a TMS9918 VDP with a simple CVBS output signal.

Simulate: System IOSEL signals

Circuit:

Complete the VDP composite video signal circuit

The schematic is incomplete. The VDP output signal is not connected. We need to complete the circuit and ensure a composite video output for NTSC and PAL.

Fix broken cassette input processing

As detected in #30, the design of cassette input processing is broken. Inverted connectors and overcomplicated design.

Verify space and distances for cartridge connectors

Because other elements too close to the connector could prevent the cartridge to be successfully inserted.

Simulate: CPU /WAIT signal

Double check status of unconnected logic gates

Check whether some of them can be used to buffer some signals. And check whether we need to feed logic inputs to ground.

Separate PS2 connector from adjacent ICs

Simulate: System /RESET signal

Review whether PPI should be placed closer to keyboard matrix emulator

Ensure PSG audio output signal is strong enough

As the TODO comment says in the schematic, we need to experiment with the audio output signal to ensure if is strong enough to generate an audible sound. If not, a amplifier circuit has to be added.

Provide a footprint for the MSX joystick port

CD4069 transits too slowly for clock generation

Checking the datasheet after some experiments with crystals above 10Mhz, it is clear that the transition of this NOR gate is too slow. 100ns @ 5 volts. This is causing the clock signal to be rounded instead of squared.

It would be great to find some other unbuffered NOR gate that transits quicker and use it for the clock generation.

Extend ROM from 32KB to 64KB

The slot supports that. And it makes no sense to now allow the user to write data in his ROM beyond 8000h.

Provide a initial placement of footprints in the PCB

Replace 3D shape of electrolytic capacitor by one more realistic

The current one is extremely big. 10uF capacitors are smaller.

Complete power sheet in the schematic

Including the decoupling capacitors and the mini-USB power connector.

Replace cassette 3.5 jack connectors by standard DIN

We are using 3.5 jack connectors for cassette input and output signals. It would be much better to use the standard DIN connector for that.

Add decoupling capacitors for power input

We have decoup caps for every single integrated circuit, but not for the power input. Big ones have to be added there to ensure resilience to power drops.