Hardware development question

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By NYYRIKKI

Enlighted (6016)

NYYRIKKI's picture

17-10-2013, 20:16

Hi, I hope some of you hardware experts can help me.

If I would like to build a general purpose bidirectional 8-bit I/O port for MSX (Think about for example joystick port pins 6-8 but just more wide), then what components should I be looking at? I think there must exist advanced IC's that make this easy to implement, but I just don't know them.

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By Eugeny_Brychkov

Paragon (1232)

Eugeny_Brychkov's picture

17-10-2013, 22:59

ST78C36
Probably easy to implement, but depends on what solution you are looking for - could be totally unsuitable.

Which protocol you are going to use? Who will be initiator? Who will arbiter the bus? Do you really need bi-direction, or can use 4 upstream and 4 downstream lines?

By sd_snatcher

Prophet (3642)

sd_snatcher's picture

18-10-2013, 00:21

Maybe this info can be useful to you: AFAIK, the printer port on the MSX models with a MSX-Engine >=S1985 is bidirecional.

The S1985 datasheet explicit states: "Bi-directional printer mode".

Otherwise, I would recommend a pair of 74LS573 latches plus an address decoder then.

By WORP3

Paladin (864)

WORP3's picture

18-10-2013, 00:18

It all depends if you can use programmable chips like gals or cpld or want to just use conventional logic ?

By NYYRIKKI

Enlighted (6016)

NYYRIKKI's picture

18-10-2013, 08:07

Yes, maybe I should explain my self a bit better...

I got this kind of protoboard:

... and I would like to put it to good use. I thought the most useful way would be to make it a general purpose I/O board for all the possible future projects... maybe add also some A/D converters, not sure yet. Point is that I don't always want to occupy joystick / printer port if I want to control some external device.

I don't say no to programmable chips although I have no experience on these ones... as long as they can be programmed with Willem. Just give me some good hints, what to look at. How ever SMD-components are something I would like to avoid. I would rather like to use DIP-packed.

Doing input ports & output ports separately is also ok. If they are all open collector with pull-up resistors, I can always hook them together if I really need input & output on the same pin (ie. TWI)

By NYYRIKKI

Enlighted (6016)

NYYRIKKI's picture

18-10-2013, 08:28

Just another idea... Maybe I should make it pin compatible with Arduino shields... This would give me access to lot of low cost hardware although I think in that case this should be mounted to slot expander.

By MicroTech

Champion (388)

MicroTech's picture

18-10-2013, 09:16

If still available I would use a Z80 PIO...
A Z80 family peripheral for each protoboard: a CTC, a SIO... and a DMA controller (if it could work on MSX architecture) with I/O base address configurable via jumpers (or dip switch).

By WORP3

Paladin (864)

WORP3's picture

18-10-2013, 11:06

You could also connect a 8255 using some logic chips, then you will have 24 programmable pins.

See 8255 datasheet for some explanation and vg8020 schematic to see how a 8255 is connected inside an msx.

By Jipe

Paragon (1594)

Jipe's picture

18-10-2013, 11:46

in MSX MAGAZINE a schematic use a 8255 with added socket eprom for program

1990 07 P128 CARTOUCHE I/O PPI 8255
1990 08 P128 I/O PPI AFFICHEUR A LED
1990 09 P124 I/O PPI QUIZZ
1990 10 P122 CARTOUCHE I/O PPI VERSION 2 ROM
1990 11 P124 I/O PPI CONVERTISSEUR ANALOGIQUE/DIGITAL
1990 12 P126 I/O PPI A/D MESURES DIVERSES T° V R

1991 01 P122 I/O PPI PROGRAMATEUR D'EPROM
1991 02 P122 I/O PPI PROGRAMATEUR D'EPROM PARTIE 2

By NYYRIKKI

Enlighted (6016)

NYYRIKKI's picture

18-10-2013, 15:48

Hmm... Why didn't I think of 8255? It is already a chip that we know!
The MSX Magazine connection picture also looks pretty much what I need... How ever some minor adjustments are needed as I don't like the fact that it reserves 16 valuable I/O ports and I don't think I need those condensators & other analog stuff (or do I?)

By WORP3

Paladin (864)

WORP3's picture

18-10-2013, 15:57

Can you share a link to that MSX MAGAZINE, so I can take a look at it ?
The 8255 is in fact somewhat like the engine of the msx 1 Wink

The first breadboard I ever made was a z80 with a 8255, some ram and a eprom, worked very good Wink

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