How to get HDMI with sound output on an MTX 500/512 and replace your VRAM

[Lee]

How to get HDMI with sound output on an MTX 500/512 and replace your VRAM - recently I purchased a pico9918 with VGA output for a faulty MTX machine which when it arrived simply plugged into the faulty VDP socket and gave me perfect VGA output.

Now I have ordered a HDMI version of the PICO9918 so that I can replace the current board (which I will reuse elsewhere) and get full HDMI with a sound output on my Modern Monitor or TV. 

As if this isnt enough the board has onboard memory so theres no need to use the MTX VRam at all (no more 4116 chip issues).

For those with other machines - this board auto detects the TMS VDP used by the machine and then provides perfect emulation. 

When complete I will be adding a guide to the excellent http://www.primrosebank.net/computers/mtx/mtxphoto.htm MTX website

Pico9918 boards can be purchased from https://lectronz.com/stores/visrealm

[1024MAK]

Are these modules low enough in their profile/height that the keyboard fits without touching them?

Mark

[gunrock]

I have one, not fitted yet, but from its profile it looked as though it would fit, maybe slightly higher in height that an original VDP, but much smaller than a F18A.

[Tony Brewer]

There might be an alternative fairly soon to the PICO9918 that does a lot more (and does not plug into the VDP socket).

[gunrock]

Ooooh, intriguing! Tell us more, Tony (nice to see you back, BTW).

[Tony Brewer]

Thank you, Steve. More info:

Recently I have finished and successfully tested a Z80A CPU emulator using one core of a Parallax P2 microcontroller that supports all 38 pins. This means I could replace a real Z80A CPU (3.5-4MHz) with a P2-based PCB and the first system I want to try this on is my MTX512. The P2 has 512KB of shared RAM and the device could replace all ROM & DRAM and the VDP & VRAM. It would have a DVI/HDMI socket and would be alternative to the PICO9918. The P2 can output digital video directly from any 8-pin subset of its 64 pins and 75 ohm 1V analogue video directly from each pin using an internal 8-bit DAC. (The PICO9918 has three onboard external 4-bit DACs to generate VGA and needs a dongle to convert VGA to HDMI.) My device could emulate the ZX Spectrum and other systems. I have also written a single-core 8086 emulator and I envisage the device booting up into MS-DOS although that has not been tested yet.

[Bill B]

I quite like the Propeller chips, however it is probably possible to do the same with the Raspberry Pi RP2350.

• The RP2350 has hardware support for HDMI.
• It certainly runs the Z80 emulation from MEMU.
• The B version has enough GPIO to interface to the entire Z80 address and data buses as well as HDMI output.
• Cheaper than the Propeller 2.

A few years back I was playing with the idea of an MTX expansion based on the original RP2040, but Martin & Dave beat me to it with the MFX with similar spec.

I recently acquired a couple of PGA2350 break out boards with the idea of looking at HDMI output for the MTX. Althogh how long it will take me to make any progress on that I don't know.

[Tony Brewer]

Hello Bill, although more expensive the eight-core P2 can do more than the dual-core RP2350. I really like the P2, partly because I designed some of it! Your use of the original Propeller for the MTX PS/2 keyboard interface led me to look at the Parallax forum, where I discovered the P2 was still being designed with input from people around the world. I joined the forum and a high percentage of my suggestions were accepted by Chip Gracey of Parallax. The P2 has features that it would not have had I not become involved, almost by accident. Re HDMI, this was added after the first small batch of chips, Rev. A, were tested and could run at 250MHz and higher (180MHz was the design minimum).