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Changes in release 18:
----------------------
* Cleanups to it synthesizes correctly under Quartus II 5.1 SP2.

* For the parallel printer, don't use BREAK as end of job marker; it
  turns out too many modern serial ports -- especially USB ones --
  don't correctly handle an incoming BREAK.  Instead, turn FF into FF
  FF and use FF 00 as end of job.  This is done in hardware, so the
  firmware shouldn't notice.  abcprintd has been changed accordingly.

* In abcprintd, print "box" (ASCII 127) as a solid dot; looks better
  in standard PostScript Courier.

* Update the Z80 assembler, and include it in the release.

* This file changed from ISO-8859-1 encoding to UTF-8 encoding.


Changes in release 17:
----------------------
* Fix using SW3 as turbo button (broken in release 16.)


Changes in release 16:
----------------------
* Support the ABC80 sound generator.  The original ABC80 had an
  SN76477 semianalog synthesizer chip, largely crippled by using fixed RC
  circuits for its adjustables.  For the FPGA, emulate the operation
  using digital logic, but I believe the correspondance should be very
  good, at least to the extent that the real SN76477 matches the
  datasheet.  There is clearly *some* differences, or "out 6,255"
  would be silent on ABC80.  I simply made a guess as to how those
  sounds should be generated.  If someone with a real ABC80 could
  record a set of files of all 128 sounds I might be able to get even
  closer.

  1 REM This program plays all 128 sounds in order
  2 FOR I%=1% to 255% STEP 2%
  3 GET Z¤
  4 PRINT I%
  5 OUT 6%,0%,6%,I%
  6 NEXT I%
  7 GET Z¤
  8 OUT 6%,0%

* The display now shows the frequency in MHz by default.

* The LEDs can now be controlled programmatically if desired.

  OUT 148,X    X = 1 to control single LEDs + 2 to control display
  OUT 149,L    Sets the individual LEDs
  OUT 150,A    Sets the right display (units)
  OUT 151,B    Sets the left display (tens)

  All of these can be read back via INP(port), too.

* Centralize all the non-ABC-compatible register handling (MMU, turbo,
  LEDs.)  The turbo can now be read back (via INP(144)), in addition
  to the MMU registers which have always been readable.

* For those sick enough to want it, the cassette port is now connected
  to the following pins on Prototype Connector 1 (J11):

  Relay   - pin 29
  Output  - pin 28
  Input   - pin 38
  Ground  - pin 26, 30 and 40

  These signals are 5V and TTL-compatible.  +5V is available on pin 2
  of J12.  See page 20 of the "Nios Development Board Reference
  Manual, Cyclone Edition" (version 1.0).

Changes in release 14/15:
-------------------------
* Make the Ethernet controller available to the ABC80.  The Verilog
  for this is a bit ugly, because I really wanted to do something that
  could be implemented on a real ABC-bus card, but the Ethernet chip
  on the Altera board shares a bus with the memory.

  The Ethernet chip is an SMSC 91C111 controller; it has 128
  byte-sized registers, divided into 8 banks of 16 registers each.
  This is implemented as follows:

  OUT 1,25    - hardware select
  OUT 2,R*8+B - select register R of bank B
  OUT 0,data  - write data from selected register
  INP(0)      - read data from selected register

  WARNING: If you write the address select register (bank 1,
  register 3) then you will need to power cycle the board before you
  can access the Ethernet chip again.

* Support DBLE/NRML (141, 140) on the video display -- it should now
  have all the capabilities of the ABC800C video unit, plus black text
  and being able to press SW0 to reveal hidden text.

  As I kid, I always wondered how DBLE/NRML were implemented in
  hardware.  The answer is, it's a pain!

* Make the printer interface closer to the original ABC80 Centronics
  card.  See data/printer.asm and printer.v.


Changes in release 13:
----------------------
* Fix bug introduced during port to msxz80asm that would cause the
  comma (,) key, 44 decimal, to give a capital (D), 0x44 hex.


Changes in release 12:
----------------------
* Switch from the horrible "masm" Z80 assembler to msxz80asm:
  http://savannah.nongnu.org/projects/z80asm/

* Use Write and Verify when writing to the CompactFlash card.


Changes in release 11:
----------------------
* CompactFlash mystery solved: there is a cf_power pin which turns off
  power to the CompactFlash card on the board!  It was left floating,
  which apparently means the power supply to the CF card worked *most*
  of the time... apparently not always.  Tie this pin to VCC seems to
  work.

* Cleaned up the generation of chargen.mif a bit.  Also generate .bas
  files to select Danish/Norwegian or International (= US) charset.


Changes in release 10:
----------------------
* Bang hard on getting the CompactFlash interface more stable.  I
  still get data corruption on cards after they have been used a while;
  unfortunately it seems to be a bug on the cards themselves and I don't
  know how to work around it.

* Remove some old debugging code in T80PIO.

* Four levels of speed control: 3, 6, 12, 25 MHz.
  out 144,0 = 3 MHz, out 144,1 = 6 MHz etc.

* New LED assignment:

  LED 0 - disk (CF) activity (for real!)
  LED 1 - disk selected (like the old LED 0)
  LED 2 - CF card in slot
  LED 3 - CAS: relay    (OUT 58,32)
  LED 4 - CAS: data out (OUT 58,64)
  LED 5 - turbo 3 (25 MHz)
  LED 6 - turbo 2 (12, 25 MHz)
  LED 7 - turbo 1 (6, 12, 25 MHz)


Changes in release 9:
---------------------
* Add support to use serial port B (DEBUG) as a lame printer port.
  Since this port supports no handshake, at least on the board I have
  (Altera Nios Development Kit Cyclone Edition), it simply prints
  at default 115200 baud.  Since serial printers are virtually extinct
  I am using a program running on a Linux box to actually send the
  data to my printer; see tools/abcprintd.c.

  The hardware interface is as follows:

  OUT 1,24     - hardware select
  OUT 0,<byte> - send data byte
  OUT 2,<time> - send BREAK for time+1 bit times
  OUT 3,L,4,H  - set baud rate to 25000000/(H:L+1)
  INP(1)       - bit 0: sending byte
	         bit 1: sending break
		 bit 2: handshake active (not currently used)

  The idea is to wait until port 1 is zero before doing anything.

  The printer ROM sends BREAK on CLOSE, so that the other side knows
  that it can send the data to the printer now (job separator.)

* The top half of the Printer Option ROM area (7800h-7BFFh) is now
  RAM; the idea is to move the UFD-DOS poke variables there
  eventually.

  (UFD-DOS was actually the operating system for ABC800, not ABC80.
  I found a port of it to ABC800 in ABC-Klubbens programbank; this is
  good since the older ABC80 DOS wouldn't have supported "hard drives"
  or subdirectories.)


Changes in release 8:
---------------------
* A whole bunch of changes in version 7 was in the programming files,
  but hadn't actually been checked into the published sources!  In other
  words, the source code was wrong, and I actually ended up having to
  re-debug the CompactFlash controller from scratch.  Fix a whole bunch
  of glitches.

* Update the sources for Quartus II version 4.1 compatibility.

* New LED assignment:

  LED 0 - disk (CF) activity (for real!)
  LED 1 - disk selected (like the old LED 0)
  LED 2 - CF card in slot
  LED 3 - unused
  LED 4 - unused
  LED 5 - CAS: relay    (OUT 58,32)
  LED 6 - CAS: data out (OUT 58,64)
  LED 7 - turbo (25 MHz)


Changes in release 7:
---------------------
* Make the "80-character BASIC patch ROM" available regardless of the
  memory type; it's now enabled by bit 15 in the MMU physical page
  number.  Writes always go to the target memory type, but reads come
  from the patch ROM if the address matches and it's enabled.

  -> Note: This means the default memory map 1 isn't usable to load
     something that shouldn't be patched, such as the checksum 11273
     BASIC or a BASIC II.  If so, the following program will "scrub"
     map 1 and turn off the patch bits for all the entries:

     1 FOR I%=0% to 63%
     2 OUT 128%,I% : OUT 129%,1%
     3 OUT 130%,INP(130%) : OUT 131%,INP(131%) AND 127%
     4 NEXT I%

* Accordingly, change the "hyperspace" memory type to 7, and allow
  bits [7:0] of the physical page to determine what byte gets
  returned.


Changes in release 6:
---------------------
* Run at 25 MHz in turbo mode (3 MHz in non-turbo mode.)
  
  -> At 25 MHz the standard key repeat rate is probably too fast.
     In ABC80 keyboard repeat is done by timing loops in the BASIC
     interpreter; this can be dealt with by loading the BASIC into RAM
     and modifying it.

     The following program can be used to copy the BASIC into RAM:

     1 POKE 65408%,175%,111%,103%,95%,87%,79%,6%,128%,62%,4%,211%,132%
     2 POKE 65420%,237%,176%,62%,21%,211%,132%,201%
     3 Z%=CALL(65408%)

   Note that when the BASIC is in RAM it is no longer automatically
   switched between 40- and 80-character mode.  It would require MMU
   changes to make that happen automatically; I might add that later.

   The delay before keyboard repeat is at bytes 767 *and* 816
   (standard is 70); the delay between repeats is at byte 783
   (standard is 8).  I find the following rather usable at 25 MHz:

   4 D%=255% : R%=32%
   5 POKE 767%,D% : POKE 783%,R% : POKE 816%,D%

* *Actually* fix the clock generator!!

* Add keybindings: Home = Ctrl-Ö, End = Ctrl-Ä, PgUp = Ctrl-Å,
  PgDn = Ctrl-Ü, Delete = Ctrl-D, Insert = Ctrl-F.  This matches the
  keybindings used by the TED text editor.


Changes in release 5:
---------------------

* Up and Down keys now return Ctrl-W and Ctrl-Z.  If Ctrl is pressed
  or Scroll Lock is pressed, Left and Right return Ctrl-A and Ctrl-S
  instead of Ctrl-H and Ctrl-I.  Backspace and Tab always return
  Ctrl-H and Ctrl-I.

* Add a turbo button (sw3) that switches between 12.5 MHz and 3 MHz.
  Turbo can also be controlled with OUT (144),<turbo>.

  -> The design should be able to handle 25 MHz, but it would require
     trimming the CPU -> MMU -> SRAM -> CPU path.

* Fix the clock generator so it generates 50 Hz and 7812.5 Hz
  correctly.


Changes in release 4:
---------------------

* Handle the case where the CompactFlash card is removed from the
  socket a bit saner.

* The firmware requires masm-0.1-hpa2 to assemble (yet another bug in
  this horribly broken assembler fixed.  Really need to find a better
  one.)

* 80 character screen is now the default.


Changes in release 3:
---------------------

* 80-column mode now properly supported, including switching the BASIC
  ROM.

* The 7-segment LED is used as a substitute for the sound generator.