ZX 128 - second screen
ZXNet echo conference «hardware.zx»
Hello, All
The question is this: in #7FFD, bit 3 is responsible for selecting the active screen.
Do I understand correctly that the second screen is used when the 3rd bit is set
#7FFD and the seventh printed page? Set _only_ 3rd bit or _only
is enabling_page seven not enough to change screens?
Hello icebear
ice> in #7FFD bit 3 is responsible for selecting the active screen
It would be more correct to say “for displaying the screen”. The bit value determines which
display screen.
ice> Set _only_ the 3rd bit or _only_ enable_ the seventh page
ice> is not enough to change screens?
Page 7 should only be included in the overlay area (C000-FFFF) if
the need to change something there. Relatively speaking, at the same time you can
use 64K+6912bytes at the same time - the screen will be displayed without being in
CPU direct addressing areas.
Hello Sinus
Sin> icebear
Sin>
Sin> The 3rd bit #7FFD is responsible only for the sampling address when displayed.
Sin> this has nothing to do with the current page.
What current page are we talking about? I was talking about the current (active) screen,
whose information is displayed.
Sin> i.e. what you wrote in your last post is almost correct.
What does "almost right" mean?
Hello Sinus
Sin> and I'm probably talking about something else. :mad:
Then call a spade a spade :)
Sin> ULA does not connect any cans.
Sin> ULA simply takes information from the required memory location (the 3rd bit is mapped to the bus
Sin> addresses)
Sin>
Sin> this is not quibbling over words, just if ULA really
Sin> “connected” the desired jar, and then returned it as it was, strongly
Sin> the controller circuit would become more complicated.
This is just nitpicking with words :) Okay, next time I’ll frame it in
quotes so that there are no misunderstandings. Thanks for the info.
Hello spensor
spe> Page 7 must be included in the overlay area (C000-FFFF) only
spe> if necessary, change something there. Relatively speaking simultaneously
spe> you can use 64K+6912 bytes at the same time - the screen will be
spe> displayed without being in the direct addressing area of the CPU.
That is in other words, ULA itself connects when displaying information on the screen
the desired jar depending on the value of the 3rd bit? What if I want to write in
second screen, I have to turn on the 7th bank, right?
Hello, Maksagor
> P.S. Question from here: you and the team at one time AZX-Monstrum
> designed, so why are there gaps in such elementary moments
> come across?
Designed - that's a big word. I already wrote that they “designed” it then. A
the answer to your question is simple: the last Spectrum I had was 48K (that was the end
94th and it was a Brest Byte with a disk drive), so I’m practically not with the 128th
encountered. During the AZX days, I also recruited people for what they would do
nodes about which I either know nothing or very little (what would be faster to do, but
not what they would do for me). Plus now there is a break of almost 6 years. So
This point is elementary for those who have already encountered this at least once. Then I
I gave up earlier than I started studying. Now I looked at different diagrams and decided
check yourself.
Hello icebear
ice> Which current page are we talking about? I talked about the current (active)
ice> screen whose information is displayed.
I'm probably talking about something else. :mad:
about which page? about the one that is currently “imprinted” in the address
CPU space from #C000 to #FFFF.
> What does "almost right" mean?
> When displaying information on the screen, ULA itself connects the required bank
> depending on the value of the 3rd bit
ULA does not connect any cans.
ULA simply takes information from the required memory location (the 3rd bit is mapped to the address bus)
This is not a quibble with words, it’s just that if ULA really “connected”
the desired jar, and then returned it as it was, the scheme would have become much more complicated
controller.
Hello icebear
icebear
The 3rd bit #7FFD is responsible only for the sampling address when displayed.
it has nothing to do with the current page.
those. What you wrote in your last post is almost correct.
Hello icebear
ice> That is. in other words, ULA itself while displaying information on the screen
ice> connects the desired jar depending on the value of the 3rd bit? What if I
ice> I want to write on the second screen, I need to turn on the 7th jar
ice> so?
Yes, definitely. Otherwise, where will you add bytes using the LD, LDI(R) and
others? Of course, by “typing” page 5 or 7 into the address space. But
They can be displayed without being imprinted.
P.S. Question from here: you and the team designed AZX-Monstrum at one time,
So why are there gaps in such elementary moments?