Beeb-related questions I'd like answered
========================================

There are lots of things you need to know to write an emulator that
aren't sufficient well explained in the User Guides and manuals.
If you know the answer to any of these questions, please e-mail me
<james@hermione.demon.co.uk>.

Also, if you can help in any way by providing documentation, software,
hardware -- anything relevant, really, I'd like to hear from you. I
have a Beeb at home, but I'd like to extend the emulator to cover the
Electron and Master series of machines -- I have no documentation on
these, so if you have anything sitting in the attic or the back of a
cupboard gathering dust that you might be willing to donate or exchange
for a small sum, please get in touch. If enough people ask, I'll try one
way or another to convert the emulator to work under DOS as well.

Anyway, to the questions...


o What are the initial states of the 6850 ACIA registers ?

  That is, when the machine is powered up, before the CPU starts
  executing the OS.  Presumably they have a fixed power-up state ?


o When the 6850 ACIA does a master reset, are the parity error and
  framing error flags cleared ?


o What values are returned when the 6845 CRTC registers are read ?

  The Advanced User Guide says that the register R0-R13 are
  write-only.  There's some software (Repton, Pharoah's Curse, Penguin)
  that does try to read these registers however.  I've been told that
  R12/R13 can be used to read whatever value was written into them.
  Is this true for all the registers ?  If not, what values are returned
  when reading the write-only registers ?


o What's the initial configuration of the Analogue-to-Digital converter
  on power-up reset ?

  That is, what channel does it start doing a conversion on, is it in
  ten- or eight-bit conversion mode, is the ADC busy and is a conversion
  marked as complete ?


o What are the initial values of all the CRTC registers ?

  Before the OS sets them all up correctly so that it's actually possible
  to see the display.


o What's the initial power-up state of the 8271 FDC ?


o What's the initial power-up state of the Econet controller ?


o What's the initial power-up state of the serial ULA ?


o What's the initial power-up state of a 6522 VIA ?


o On the subject of the 6522 VIA, the manuals say that the T2
  interrupt can only be re-enabled (after it has been triggered) by
  writing to T2CH or reading from T2CL.  Is that because these actions
  also reset the interrupt flag or does this happen completely
  independently ?


o And another...  Read/Write of the ORA clears the interrupt flag
  in the IFR.  Does Read/Write of the non-handshaking copy of ORA do the
  same thing ?


o What are the mark and space periods of flashing text in teletext mode ?


o What is the power-up state of the Tube ULA registers ?


o What is the power-up state of the Video ULA registers ?


o What values are returned when the Video ULA registers are read ?

  The Advanced User Guide says that the registers are write-only.



