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(I apologize my Tarzan-like english...)
Here there are some informations about MSX2 Hitachi MB-H3.
If you have some cool info about this rare MSX2 and be pleased in share it, write to me.
And if you "just" have one write to me too. ;)
MSX2 Hitachi MB-H3
RGB connector
RGB MSX2 Hitachi MB-H3 connector
1 R
2 G
3 B
4 CSync
5 +5V
6 Audio
7 +5V
8 GND
7 6
3 8 1
5 4
2
(View from female DIN-8 connector at MB-H3 back)
For informations on what monitors can be compatible and schematics of the generally required sync separator, take a look in MSXPró site.
Expanding the VRAM
Disclaimer: use this informations under your own risk.
MB-H3 was manufactured originally with just 64kb of VRAM, but we can easily upgraded it to 128kb. For this we just need some solder iron practice, 2 DRAM 4464 (64kb x 4 bits) or compatible and one 33 Ohms resistor (orange,orange,black).
I find in one local parts provider the DRAM ICM4464 by Itautec (Brazilian) for approximately U$1.00 each. Warning: there are another IC with 4464 number in designation body, but this have 28 pins.
4464 pin assignment (source: http://www.qsl.net/yo5ofh/data_sheets/mem-ram.htm):
64kx4 DRAM.
+---+--+---+
/OE |1 +--+ 18| GND
D0 |2 17| D3
D1 |3 16| /CAS
/WE |4 15| D2
/RAS |5 4464 14| A0
A6 |6 13| A1
A5 |7 12| A2
A4 |8 11| A3
VCC |9 10| A7
+----------+
With parts in hand, just assemble the two DRAMs in IC19 and IC20 reserved positions. The resistor must be assembled in R39 position.
IC19 and IC20: DRAM 4464
R39: 33 Ohms
Check the connections, and if there's short-circuit exhaustively, clean it, etc. Connect the mainboard to keyboard and source, and voilà.. its, everithing!
Put the MB-H3 to work and it must display "VRAM: 128kbytes" in first splash-screen. Better than this test, if you have DOS, run 'TestRAM' by Adriano Cunha downloading in his site (A&L Software), to test every byte of VRAM.
Have fun!
Sources: V9938 manual.
The touch-pad
The MB-H3 touch-pad obey MSX standard, so, to play with it, we can use BASIC and/or BIOS calls.
In BASIC, for example:
5 REM six lines graphics proggie
10 SCREEN5
20 IF PAD(0)=0 THEN 40
30 PSET (PAD(1),PAD(2)),C
40 IF PAD(3)=-1 THEN CLS
50 GOTO 20
where:
PAD(0) returns 0 (zero) if the pen are up and -1 if down.
PAD(1) returns x coordinates.
PAD(2) returns y coordinates.
PAD(3) returns 0 (zero) if blue button are not-pressed and -1 if pressed.
But for correct usage you need to put the switch next the joystick 2 in correct positon (switch it to computer rear side).
Sources: AdMouse On-Line Manual (By Ademir Carchano in MSX-Projetos)
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