Another NMS 8280 MSX2+ upgrade

By Splashman

Supporter (2)

Splashman's picture

18-03-2015, 23:20

Hey guys,
stop me if you've heard this one before, but I've got a German NMS 8280 which I want to give a solid new MSX2+ upgrade (yeah, shocking). Before I get going and mod my system to death, I want to check up all the necessary steps with the experts here.

From the research I've done on Hansotten and what I understand I need the following for a complete upgrade: v9958 DVP, BASIC v3 and F4 register (for RAM and FM I've got my MegaFlash and FM PAQ carts). The DVP is ordered and on the way, and a friend will take care of wiring the ROMs.
So far so good, here are my questions:

1. v9958 rewiring:
On 8280, will the basic 1, 4, 27 to GND and 21, 58 to +5V be enough, or do I have to follow this schematic and why? If the schematic is the way to go, where are the points "pin 1" and "7010 pin 28" located?

2. ROMs
I guess the "German MSX BASIC V 3.0 ROMS made for Franz Schiefer Austria and used in the NMS8280" should be good to use for my German system. But before I write them, I would like to set them up with a 60hz default mode with optional 50hz mode when the H key is pressed, as discussed here.

NYYRIKKI wrote:

Needed modifications to NMS8250 SUB-ROM:

#0422: 8C,3E
#3E8C: CD, 3C, 06, DB, AA, E6, F0, F6, 03, D3, AA, DB, A9, E6, 20, C8, AF, 32, E8, FF, C9

Functionality:
While boot logo is displayed, push "H"-key down untill beep to start in 50Hz mode, otherways 60Hz mode will be selected.
If you want to change also boot logo to 60Hz, put 0 to #2B56

Can I apply this exact code change to the new subrom, or is it different for MSX2+?

3. F4 register
What is it and do I really need it just for games? :P
This schematic really confuses me because I don't know where the different end points lead to.

That would be it, or did I miss anything?
Thanks in advance!

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By RetroTechie

Paragon (1563)

RetroTechie's picture

19-03-2015, 04:44

Welcome to MSX.org forum, Splashman! Running Naked in a Field of Flowers

First off: the simple fact that you're asking these questions, suggests it may be wise NOT to embark on this project. Or if you do, chances are good @ some point you'll find yourself with a non-working machine. With no-one in sight to fix it. Evil

1. Myself I'd go with a V9958 Video Display Processor. Wink The hardest part is unsoldering the V9938 without damaging the circuit board. There's 2 options here:

a) Unsolder (either pin by pin, or all pins at once using some professional tool). But even then you may damage the circuit board.
b) Simply cut all pins, and remove remains. Has the highest chance of keeping the circuit board in 1 piece. Bit of a shame for the V9938 tbh, but replacements are not that expensive or hard to find these days. So it's valid to consider this method even when the chip to replace is an MSX2 VDP.

If you can find a 64 pin "shrink DIP" IC socket, I'd use one. That allows you to put a V9938 back in after the unsoldering / solder IC socket job, and verify that everything still works. Required changes for accepting a V9958 are relatively easy then. And thus (if needed) easy to reverse, too.

V9958 databook has a nice overview of which pin functions are changed compared to a V9938. And there's a number of descriptions floating around how to wire up those pins. The NMS8280 isn't the easiest machine to do this VDP swap on (due to all the digitize / genlock circuitry attached to the VDP), but not as difficult as some old magazine articles suggested.

The V9958 is somewhat more sensitive regarding its 5V supply (ehm.. -ies). But I'd skip on using an extra regulator like a 7805. A small coil + some capacitors will do the same job. And not need +12V, which you DON'T want near the VDP anyway!

2. F4 register is a 1 bit I/O port (bit 7 on I/O address F4h). Original MSX2+ / Turbo-R machines use this to distingish between a "hard" reset (power cycle or reset button pushed) and a "soft" reset (jump to BIOS ROM address 0). In the first case, boot logo is shown and memory counted destructively. Which I suspect most MSX users will regard as a feature. For a soft reset, this is skipped so the reboot is faster.

Imho the utility of this is questionable, and one can implement in a number of ways:

a) Implement F4 port to work exactly as in an original MSX2+. Which minimizes required ROM changes.
b) Implement F4 port, but with hw reset state reversed. Which may simplify the hardware, but at least requires flipping some bits in the new ROMs. From what I've seen, quite a few MSX2+ conversions work this way.
c) Not implement F4 port, and always do boot logo + memory count on each reboot.
d) Not implement F4 port, and remove boot logo + memory count. Which lets you get away with using fewer ROMs. But of course you'd not have the nice 2+ boot logo then. Crying

As you'll guess, each approach needs different ROMs. Each MSX2+ ROM set out there assumes / implements one of the above approaches. Date format / keyboard layout etc further complicates things. Whatever ROMs you'd decide to use, I suggest testing them very thoroughly on emulator(s) before burning to EPROM(s).

Both MSX2+ ROMs and F4 register are optional - a lot of software will work with a V9958-equipped MSX2.

Before doing any modding (or even before powering up!), consider these jobs first:
1) Remove the NiCd battery. At some point it will probably leak (if it hasn't already), and nuke some board traces or nearby components in the process.
2) Replace ALL electrolytic capacitors with new ones. oO Especially those in power supply and audio/video circuitry. Original ones will be in poor condition at best, or waiting to pop & possibly take out other circuitry with it. Especially if machine hasn't been powered up in a long time. This is a hassle, but electrolytic capacitors have a limited service life, and most MSX machines are pushing it or are beyond that point... (and these capacitor issues have been documented in maaaannny places).

By o.geerdink

Hero (539)

o.geerdink's picture

19-03-2015, 07:08

Will the digitize/superimpose function work with this upgrade?

By RetroTechie

Paragon (1563)

RetroTechie's picture

19-03-2015, 08:44

Why wouldn't it? Genlock & digitizing is done by other circuitry, all the VDP does is pump the data into its VRAM. That process (+ pins / registers involved) is not among changed/deleted functions, so should work the same as with a V9938.

By igal

Master (211)

igal's picture

19-03-2015, 13:06

This is thé software solution for fix genlock synchro on vdp9958.

10 SCREEN 8,,,,,3:GOTO 10

press [CTRL+STOP] when you want for fix synchronisation.

More infos here http://www.msxvillage.fr/forum/topic.php?id=1866&pt=1

By flyguille

Prophet (3029)

flyguille's picture

19-03-2015, 17:18

RetroTechie wrote:

Welcome to MSX.org forum, Splashman! Running Naked in a Field of Flowers

First off: the simple fact that you're asking these questions, suggests it may be wise NOT to embark on this project. Or if you do, chances are good @ some point you'll find yourself with a non-working machine. With no-one in sight to fix it. Evil

1. Myself I'd go with a V9958 Video Display Processor. Wink The hardest part is unsoldering the V9938 without damaging the circuit board. There's 2 options here:

a) Unsolder (either pin by pin, or all pins at once using some professional tool). But even then you may damage the circuit board.
b) Simply cut all pins, and remove remains. Has the highest chance of keeping the circuit board in 1 piece. Bit of a shame for the V9938 tbh, but replacements are not that expensive or hard to find these days. So it's valid to consider this method even when the chip to replace is an MSX2 VDP.

If you can find a 64 pin "shrink DIP" IC socket, I'd use one. That allows you to put a V9938 back in after the unsoldering / solder IC socket job, and verify that everything still works. Required changes for accepting a V9958 are relatively easy then. And thus (if needed) easy to reverse, too.

V9958 databook has a nice overview of which pin functions are changed compared to a V9938. And there's a number of descriptions floating around how to wire up those pins. The NMS8280 isn't the easiest machine to do this VDP swap on (due to all the digitize / genlock circuitry attached to the VDP), but not as difficult as some old magazine articles suggested.

The V9958 is somewhat more sensitive regarding its 5V supply (ehm.. -ies). But I'd skip on using an extra regulator like a 7805. A small coil + some capacitors will do the same job. And not need +12V, which you DON'T want near the VDP anyway!

2. F4 register is a 1 bit I/O port (bit 7 on I/O address F4h). Original MSX2+ / Turbo-R machines use this to distingish between a "hard" reset (power cycle or reset button pushed) and a "soft" reset (jump to BIOS ROM address 0). In the first case, boot logo is shown and memory counted destructively. Which I suspect most MSX users will regard as a feature. For a soft reset, this is skipped so the reboot is faster.

Imho the utility of this is questionable, and one can implement in a number of ways:

a) Implement F4 port to work exactly as in an original MSX2+. Which minimizes required ROM changes.
b) Implement F4 port, but with hw reset state reversed. Which may simplify the hardware, but at least requires flipping some bits in the new ROMs. From what I've seen, quite a few MSX2+ conversions work this way.
c) Not implement F4 port, and always do boot logo + memory count on each reboot.
d) Not implement F4 port, and remove boot logo + memory count. Which lets you get away with using fewer ROMs. But of course you'd not have the nice 2+ boot logo then. Crying

As you'll guess, each approach needs different ROMs. Each MSX2+ ROM set out there assumes / implements one of the above approaches. Date format / keyboard layout etc further complicates things. Whatever ROMs you'd decide to use, I suggest testing them very thoroughly on emulator(s) before burning to EPROM(s).

Both MSX2+ ROMs and F4 register are optional - a lot of software will work with a V9958-equipped MSX2.

Before doing any modding (or even before powering up!), consider these jobs first:
1) Remove the NiCd battery. At some point it will probably leak (if it hasn't already), and nuke some board traces or nearby components in the process.
2) Replace ALL electrolytic capacitors with new ones. oO Especially those in power supply and audio/video circuitry. Original ones will be in poor condition at best, or waiting to pop & possibly take out other circuitry with it. Especially if machine hasn't been powered up in a long time. This is a hassle, but electrolytic capacitors have a limited service life, and most MSX machines are pushing it or are beyond that point... (and these capacitor issues have been documented in maaaannny places).

you can cut the pins with a cutter just before the pins go in the PCB, so you don't damage the 9938 that much, and can be restored later with some components wiring (just strips resistors legs and solder on what left from each pin).

By Splashman

Supporter (2)

Splashman's picture

19-03-2015, 17:42

RetroTechie wrote:

Welcome to MSX.org forum, Splashman! Running Naked in a Field of Flowers

Thanks, nice place here. oO

Quote:

First off: the simple fact that you're asking these questions, suggests it may be wise NOT to embark on this project. Or if you do, chances are good @ some point you'll find yourself with a non-working machine. With no-one in sight to fix it. Evil

Oh I know, I already half-murdered a Twin Famicom once by trying to replace an IC, so desoldering and putting the socket in there is what I'll let my friend take care of.

Quote:

V9958 databook has a nice overview of which pin functions are changed compared to a V9938. And there's a number of descriptions floating around how to wire up those pins. The NMS8280 isn't the easiest machine to do this VDP swap on (due to all the digitize / genlock circuitry attached to the VDP), but not as difficult as some old magazine articles suggested.

The databook should be easy to find, but you give a few more pointers where to find some good rewire descriptions?

Quote:

a) Implement F4 port to work exactly as in an original MSX2+. Which minimizes required ROM changes.
b) Implement F4 port, but with hw reset state reversed. Which may simplify the hardware, but at least requires flipping some bits in the new ROMs. From what I've seen, quite a few MSX2+ conversions work this way.
c) Not implement F4 port, and always do boot logo + memory count on each reboot.
d) Not implement F4 port, and remove boot logo + memory count. Which lets you get away with using fewer ROMs. But of course you'd not have the nice 2+ boot logo then. Crying

Sounds almost like a philosophical question then. I guess I could live without the boot logo if I can speed up the reboot a bit. But what I take from it is that I could do without installing the register and concentrate on ROM changes instead. In that case I'll have to figure out how to assemble the best ROM set for my machine. But I think I'll go with the VDP first and see how it goes from there.

Quote:

Before doing any modding (or even before powering up!), consider these jobs first:
1) Remove the NiCd battery. At some point it will probably leak (if it hasn't already), and nuke some board traces or nearby components in the process.
2) Replace ALL electrolytic capacitors with new ones. oO Especially those in power supply and audio/video circuitry. Original ones will be in poor condition at best, or waiting to pop & possibly take out other circuitry with it. Especially if machine hasn't been powered up in a long time. This is a hassle, but electrolytic capacitors have a limited service life, and most MSX machines are pushing it or are beyond that point... (and these capacitor issues have been documented in maaaannny places).

Right, I always forget about the caps. My machine still runs fine so far, but for how long until the caps run out is the question.

By mohai

Paladin (835)

mohai's picture

26-05-2015, 16:09

Hello,

did you do any upgrade so far?
I am modding my 8280 and I am thinking of upgrading it to 2+ too.

Adding F4 register to this machine is not difficult.
This document shows diagram for 8280.

By Alexey

Guardian (2349)

Alexey's picture

28-05-2015, 12:52

Btw, Kamil Karimov (aka Caro) made another nice project - the F4 board that can be soldered directly to Z80 CPU outputs. It has the size of Z80 and can be even put on top of it. The board has 4 logic chips and a few smd components. I have 10 of those unassembled boards, 2 I leave for myself, others I can offer for a very small price without components. But those chips and smds are easy to find. Will post a picture of the board later today.

Alexey

By mohai

Paladin (835)

mohai's picture

28-05-2015, 16:12

That could be nice.

Long ago, I got PAL chip to make F4 register.
I bought it, because they told me it was te solution to see 2+ logo in upgraded MSX 2.
As I had an nms8245 upgraded to 2+, I installed it, but I never saw logo, so I stored it somwere.
Later, I found out that logo image is in an extra ROM I did not have in my 8245, but I had lost PAL chip ... Sad