Hi,
shevek <[EMAIL PROTECTED]> was asking about the PSG:
> Last week, I wrote about MSX PSG accessing. On Commodore 64, it is
> impossible to read sound registers, so when I saw the same in MSX BASIC, I
> thought it was a hardware thing.
No, on the MSX you can both read & write PSG registers, both through
hardware & BIOS as well.
> I never tried to write to register 14, but if it is not hazardous, that is
> only good.
Sure you can't destroy MSX hardware by a simple programming trick!
(prove me wrong)
> In the tables I have at home, register 7, bit 6 and 7 are said to be port
> A/port B, and register 14 bit 6:keyboard. Does anybody know what those
> bits do?
You asked something like this earlier. I suggest you get some GOOD
documentation on MSX stuff. I can recommend the Dutch "MSX-Handboek
voor gevorderden", which gives a detailed explanation of MSX hardware
use, nicely combined with the info on support by BIOS routines or MSX
BASIC.
The MSX Technical Databook is also a very good reference (if you can
get your hands on a copy).
And ofcourse there is the MSX2 Technical Handbook, which Nestor
Soriano put online.
PSG-registers 14 & 15 reflect the general-purpose I/O-ports included
in the PSG, in the MSX these are mainly used to control the 2
joystick-ports.
Bit 6 & 7 of PSG reg.7 determine wheter these PSG ports are
read-only, or can be used as output.
Bit 6 controls this for port A (PSG reg.14) and bit 7 controls this
for port B (PSG reg. 15).
In the MSX, the use of these ports is fixed:
port A = input (bit 6 of PSG reg. 7 = 0)
port B = output (bit 7 of PSG reg. 7 = 1)
Therefore, either changing these bits has no use, or it can be that
these are hardwired this way (if the PSG is integrated in some type
of MSX-engine).
Bit 6 of PSG reg. 14 (=port A, input) is used in Japanese machines,
and indicates a type of keyboard layout.
I quote from the MSX Technical Databook:
JIS layout - "H", syllable layout - "L"
Don't ask me what it means exactly, although I do suspect it's
something different than the keyboard layout as indicated by ID-bits
in the MSX ROM.
I expect this bit will always read as "0" on non-japanese MSX
machines, and will either read always "1", or indicate some state
related to the keyboard, in Japanese MSX machines.
Similarly, bit 7 of PSG-register 15 (port B, =output) controls the
Kana LED in Japanese MSX machines (0 = on, 1 = off), but has no
effect on non-Japanese machines.
Greetings,
Alwin Henseler ([EMAIL PROTECTED])
http://huizen.dds.nl/~alwinh/msx (MSX Tech Doc page)
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