F4 Register and signal Y0 # (& HF4) in HB-F9S...

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By Dhampird

Hero (585)

Dhampird's picture

14-12-2010, 01:25

Hello, i´m looking for where is allocate my Y0 # (& HF4) Signal in HB-F9S, i´m trying to apply F4 Register to my MSX2 with V9958 and Basic 3.0 Roms, the problem is about Y0 # (& HF4) Signal.

I´m follow the F4 Register diagram from here:


I locate all point in HB-F9S to try the install but i need to locate how i can get "Y0 # (& HF4) Signal". In S1985 there is a Y0 Signal, in PIN 84, anyways i dont know if this is the real "Y0 # (& HF4) Signal", reading some Hans0 info i read that:

"F4 register which applies in the BASIC 3.0 ROM but at least be present when the V9958 VDP used in a MSX 2 computer. The signal Y0 # (& HF4) is drawn from pin 4 of IC 158 (74LS139)...."

That explain if for F4 Register intall in NMS8250/55, i get service manuals and i discover that there is not IC158, there is IC159 (74LS139), but is so difficult to extrapolate the info to my HB-F9S, there is no 74LS139 in HB-F9S, only most similar IC is 74LS157.

Later i checked HB-F700 service manual, and i found a IC 74LS139 (IC7), in that IC some pins goes to DRAM, i think, and another goes from S1985 PIN 5 (MA15) and PIN4(MA16) to the IC...

All that i checked about 74LS139 is different, i´m wonder if anyone could help me to locate "Y0 # (& HF4)" Signal in HB-F9S or explain me if i should get that signal from S1985, or will be need to combine in any IC to get another result signal...

I´m lost with this...

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By Jipe

Paragon (1366)

Jipe's picture

14-12-2010, 12:39

if you see the schematic : Latch F4. A ideia original veio do site do Hans Otten e está reproduzida abaixo

in the left part you find the schemetic for making the #Y0 (&HF4) signal 74LS138 74LS139
on pin 4 of 74LS139 #Y0 is out for the right part of schematic

By Dhampird

Hero (585)

Dhampird's picture

14-12-2010, 13:05

Thanks for reply "Jipe", then if i understood ok, this will be the correct diagram:


By Jipe

Paragon (1366)

Jipe's picture

14-12-2010, 18:28

yes is done

By Dhampird

Hero (585)

Dhampird's picture

16-02-2011, 22:26

Finally ,after a long time without being able to mount the circuit because I've been busy, I built F4 circuit according to the diagram. Now when i turn on the HB-F9s the msx boot logo dont appear and goes directly to BASIC, the same happens if i press RESET, the boot logo does not appear more, I´m wonder therefore if the F4 circuit is properly mounted. I added a jumper on the 5V line to enable or disable the circuit.

If there is another way to check that the circuit is perfectly working, like any basic line, please comment.



Thanks for help "Jipe".

By Jipe

Paragon (1366)

Jipe's picture

17-02-2011, 13:43

i make this circuit and mount in a 8235 / 39 and work fine
are you sure you have the good rom for MSX2+ ?

By RetroTechie

Paragon (1563)

RetroTechie's picture

17-02-2011, 15:38

I was thinking the same... First: check if writes to I/O port F4 (bit 7) are actually recorded (simple commands in BASIC + voltmeter on the latch's IC pin). If not, the logic isn't built correctly or doesn't work due to faulty parts/wiring.

If that works, check what state the bit goes into on a hardware reset (reset button / power up). Some ROMs used in 2+ conversion projects have this reversed from how it is for a real MSX2+. Reason being easier construction of the latch. But if ROMs used & reset state don't match... well you get the idea. Crying

By Manuel

Ascended (15970)

Manuel's picture

17-02-2011, 22:05

There are normal and inverted implementations of this register. You need a matching ROM to make it work.

Oh, I'm repeating RetroTechie.

Anyway, in the openMSX hardware config XML files you can see which type is in which machine.

By Dhampird

Hero (585)

Dhampird's picture

18-02-2011, 02:35

Well, according to my roms:

"I have not made any changes to this part of the ROM... It still reads the F4 port just like any original MSX2+, but if there is nothing connected to that I/O port it will always return 255 that causes boot logo to appear on all reboots as well. If you add this F4 port later then it will not anymore show boot logo on soft boot... The bottomline is that if you add this port later you don't need to update ROMs again."

I attached here the .roms that now i´m using in HB-F9s for if someone could help to recognize its compatibility with the F4 registration, or if they would be valid roms.

{ mod edit: removed link }

"check if writes to I/O port F4 (bit 7) are actually recorded (simple commands in BASIC + voltmeter on the latch's IC pin)"
"check what state the bit goes into on a hardware reset (reset button / power up)"

I need more specific info to try these tests, the basic commands needed, how check the latch circuit and how recognise bit state with hardware reset...

Thanks a lot for help.

{ mod edit: no links to warez! }


Enlighted (5425)

NYYRIKKI's picture

18-02-2011, 07:19

Try something like:

OUT &HF4,0:?INP(&HF4)


OUT &HF4,255:?INP(&HF4)

By caro

Champion (488)

caro's picture

18-02-2011, 13:08

I attached here the .roms that now i´m using in HB-F9s
1) With that ROM, which is established at you, this circuit will not be normal to work.
2) It is impossible in this circuit to use a signal #RESET.
The initial installation of the register #F4, should be only on inclusion of the computer.

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