What is -12V used in MSX?

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By dhau

Paragon (1570)

dhau's picture

05-01-2007, 14:36

Hello guys,

I am currently restoring a somewhat damaged Sony HB-F1. It had the power stabilizing circuitry fried, I removed it all from the board and connected +5V and GND from PC AT PSU directly to motherboard. It seems to work great, with games running with PSG and SCC sound. I understand MSX standard require +5, +12 and -12V. +5V is used for pretty much everything, +12V is used by some floppy drive controller chips and floppy drive itself (which is irrelevant for diskless HB-F1).

But what is -12V for?

How safe is it to skip it?

It is required on MSX slots, but is there any carts that use it?

Thanks in advance for your help,

-Adrian

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By AuroraMSX

Paragon (1902)

AuroraMSX's picture

05-01-2007, 14:59

MoonSound or RS232 interfaces maybe?

By dhau

Paragon (1570)

dhau's picture

05-01-2007, 15:14

I hope sunrise can tell if MoonSound needs -12V.

RS232 only uses 5V.

By Edwin

Paragon (1182)

Edwin's picture

05-01-2007, 16:04

I'm actually not so sure that the Moonsound needs 12V at all. In Bussum the OCM was running with a Moonsound. But I can't find any power conversion circuitry on the OCM at all. I can't imagine that the opl4 actually needs more than 5V, so if 12V is used, then it may just be for amplification. In which case a lower voltage may work as well.

By HansO

Paladin (672)

HansO's picture

05-01-2007, 17:07

RS232 only uses 5V.

RS-232-C output and control lines swing between -25 - 3V and +3 + 25 V. Often + and - 12 V is choosen as a good compromise. 0 V is 'undefined'.

So MSX serial interfaces require at least the - 12 V and, because it is available in the standard, are using + and -12V.

By dhau

Paragon (1570)

dhau's picture

05-01-2007, 17:09

So basically 12V can be pretty much avoided?

By Manuel

Ascended (18404)

Manuel's picture

05-01-2007, 20:29

Can someone of Bazix shed a light on this? (I know they are reading these forums as well.)

By Sonic_aka_T

Enlighted (4130)

Sonic_aka_T's picture

05-01-2007, 21:21

I heard a few older modems use -12V, never actually confirmed this tho. I suppose you could test this on an OCM... Smile

By Latok

msx guru (3861)

Latok's picture

05-01-2007, 21:24

Snout told me the 1chipMSX has a voltage convertor on board...How does that look like? I can check my 1chipMSX.

By Sonic_aka_T

Enlighted (4130)

Sonic_aka_T's picture

05-01-2007, 22:17

Snout told me the 1chipMSX has a voltage convertor on board...How does that look like? I can check my 1chipMSX.It's coded in FPGA: V12=V5+7V Tongue

By HansO

Paladin (672)

HansO's picture

05-01-2007, 22:21

I heard a few older modems use -12V, never actually confirmed this tho. I suppose you could test this on an OCM... Smile
The Sunrise RS232 uses + and -12V.

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