To those who have a Sony HB-G900 | MSX Resource Center

Por Manuel

Ascended (19332)

04-05-2010, 15:46

I expect it to return 83.

See http://map.grauw.nl/resources/msx_io_ports.php#subslot

Por Eugeny_Brychkov

Paragon (1232)

04-05-2010, 15:49

I expect it to return 83.
See http://map.grauw.nl/resources/msx_io_ports.php#subslot

It needs proving. In theory it should return 83, but practice depends on the internal connections between chips. As I said, per service manual, both main memory (with "positive value" ) and secondary slot selection register ("inverted value" ) should output to the data bus, resulting 0 to be read.

Por DD

Expert (88)

04-05-2010, 16:04

Shouldn't CAS2/E mask this address for this DRAM?

Por Eugeny_Brychkov

Paragon (1232)

04-05-2010, 16:16

My mistake. It is not NMS8280, I am talking about Sony HB-G900! How can I change the title of the thread?

Por DD

Expert (88)

04-05-2010, 16:18

Wow in a NMS8280!?

Por DD

Expert (88)

04-05-2010, 16:21

Oops, don't know how to change the title actually. Er, any moderator around here?

Por RetroTechie

Paragon (1563)

04-05-2010, 17:16

The Sony G900 (without -A) has expanded slot 0 with various ROMs (video utility, RS232 stuff) in it, and RAM in *not expanded* slot 3.
With that slot (RAM) in page 3 (=the normal situation in DOS / BASIC), memory location FFFFh is ordinary RAM, not a secondary slot register. Read: value not interesting, nothing happens if you write there.

Although there's at least 1 HB-G900 out there which has expanded slot 3 instead of 0 (sorry...)

Shouldn't CAS2/E mask this address for this DRAM?
There is no MSX engine that produces this signal in the HB-G900; in fact there is no MSX engine whatsoever in this machine (just ungodly heaps of 74LSxx parts and analog circuitry) ...

Por Eugeny_Brychkov

Paragon (1232)

04-05-2010, 17:57

The Sony G900 (without -A) has expanded slot 0 with various ROMs (video utility, RS232 stuff) in it, and RAM in *not expanded* slot 3.
With that slot (RAM) in page 3 (=the normal situation in DOS / BASIC), memory location FFFFh is ordinary RAM, not a secondary slot register. Read: value not interesting, nothing happens if you write there.
Thanks Alwin, I missed this. By the way, there are some mistakes on the diagram regarding this... Thus if main memory would be in slot 0 which is expanded then logic would mask FFFFh for memory.

... in fact there is no MSX engine whatsoever in this machine (just ungodly heaps of 74LSxx parts and analog circuitry) ...
Is it good, or bad?

Por RetroTechie

Paragon (1563)

04-05-2010, 18:46

Thus if main memory would be in slot 0 which is expanded then logic would mask FFFFh for memory.
Just picked up the schematic, and to be honest I'm not so sure FFFFh is excluded from slot 0-x signals. But there isn't any memory that responds to FFFFh location in 0-x slots (just 0000-7FFF, or 4000-7FFFh ranges), so never a conflict with secondary slot register.

Is it good, or bad?
Ugly. On the plus side: there is nothing you can't do in this machine (just takes a lot of work) ...

Por Eugeny_Brychkov

Paragon (1232)

04-05-2010, 18:59

Ugly. On the plus side: there is nothing you can't do in this machine (just takes a lot of work) ...
And that's why I love it. You can connect anywhere in the pc and make your own device or modify existing. If something fails, it is fun to find out what's wrong instead of blaming single chip.