M/C Part 14

                             MEMORY
                             ------

The 64k addressing range is split into four 16k pages, of which
there are 32 Ram and 2 ROM.

For clarity, I shall refer to the memory map used in the
technical manual:

         0000    4000    8000    C000    FFFF
            _______________________________
           |       |       |       |       |
           |   A   |   B   |   C   |   D   |
           |_______|_______|_______|_______|

           \______  ______/ \_____  ______/
                  \/              \/
             Lower memory     Upper memory
              (See lmpr)       (See hmpr)

NB. Only sections A and C can be controlled - B is always the
page after the one in A and D is always the page after C.

                             PORTS
                             -----

lmpr:      D0  \
           D1   \
* 250 *    D2    >     Page in section A of memory map.
           D3   /
Read/      D4  /
Write.     D5          0 for ROM0 in section A. 1 for RAM page.
           D6          0 for RAM in section D. 1 for ROM1.
           D7          RAM in section A write protected when
                       this bit is high.

hmpr:      D0  \
           D1   \
* 251 *    D2    >     Page in section C of memory map.
           D3   /
Read/      D4  /
Write.     D5    \     In mode 3, used as D2 and D3 of colours.
           D6    /
           D7          When high, extra memory is used for
                       sections C and D.

vmpr:      D0  \
           D1   \
* 252 *    D2    >     Page to use for video display.
           D3   /
Read/      D4  /
Write.     D5    \     Screen mode (0-3).
           D6    /
           D7          I/O bit for Midi.

Sound:     Address port 511 & data port 255. See Technical
           Manual for extra information. Write only.

Midi:      Outputs through port 253. See Tech Manual.

Border:    D0  \
           D1   \
           D2    \     Border colour (0-15)
       __\       /
      |  /      /
      |    D5  /
      |    D6          Midi operation allowed if high.
      |    D7          In modes 3 & 4, disables screen if high.
      |
      |   __________________________________________________
      |  |                                                  |
      |__| D3    -     Output bit for ~mic~, normally high. |
         | D4    -     Output bit for ~beep~, normally low. |
         |__________________________________________________|

           (Write only)

Line:      Write only register addressed through port 249. When
           TV scan reaches Y line specified by this register, an
           interrupt is generated. Range of 0-191. Any other
           value disables this function.

Palette:   Base port 248. Registers from 0-F correspond to
           palette colours, addressed using 248 as the LSB and
           the register no. as the MSB.

           Each register is write only: the colour is defined as
           follows:

           D0   \                                  / B
           D1    >     Least significant bit of:  <  R
           D2   /                                  \ G
           D3          Half bit brightness on all colours.
           D4   \                                  / B
           D5    >     Most significant bit of:   <  R
           D6   /                                  \ G
           D7

Attributes register: Read only from port 255. Returns the
           attributes of the currently displayed cell in modes
           1 & 2, and the third byte in every four in modes
           3 & 4.

Keyboard:  Base port 254. MSB specifies line of keys to scan.
           Read only.

           D0  \
           D1   \
           D2    >     First 5 keys. Low when pressed.
           D3   /
           D4  /
           D5          Light pen strobe/ serial input bit.
           D6          Input from ~EAR~ of cassette recorder.
           D7          Status bit showing external memory on/off

           MSB on A8 - A15 gives keyboard lines as follows:-

                                 1   2  3  4  5   6   7   8

 A8 low (others high) = FE     SHIFT Z  X  C  V  F1  F2  F3
 A9 low               = FD     A     S  D  F  G  F4  F5  F6
A10 low               = FB     Q     W  E  R  T  F7  F8  F9
A11 low               = F7     1     2  3  4  5  ESC TAB CAPS
A12 low               = EF     0     9  8  7  6  -   +   DEL
A13 low               = DF     P     O  I  U  Y  =   "   F0
A14 low               = BF     ENTER L  K  J  H  ;   :   EDIT
A15 low               = 7F     SPC  SYM M  N  B  ,   .   INV
none low (all high)   = FF     CTRL  /\ \/ <  >

Status:    Read only from port 249. Keys similar to Keyboard
           port.

           D0  \                                      LINE
           D1   \                                     COMMS
           D2    > When low, indicates the interrupt. MIDI-in
           D3   /                                     FRAME
           D4  /                                      MIDI-out
           D5   \
           D6    > Keys 6, 7 and 8 as listed above.
           D7   /

Midi-in:   Read only port 253 which generates an interrupt (see
           above) when read. Data must be read by the CPU before
           the next interrupt.

Pen:       LPEN (248) - gives X coordinate.
           HPEN (504) - gives Y coordinate.

           LPEN:  (additional)

           D0    Inputs D0 of current colour (as in palette no).
           D1    When high, shows that a byte is being
                 transmitted through Midi-out.

                          SCREEN MODES
                          ------------

There are four screen modes available.

MODE 1.    Spectrum emulation.
           192 pixels vert * 256 horiz.
           6k bit-mapped (0-paper, 1-pen)
            +768 byte attribute file. Each attribute covers 8*8
            pixel cell. Worked as follows

           D0   \
           D1    >  Pen colour (0-7)
           D2   /
           D3   \
           D4    >  Paper colour (0-7)
           D5   /
           D6       Bright on/off. (D4 of pen AND paper).
           D7       Flash on/off.

MODE 2.    Similar to mode 1.
           192 pixels vert * 256 horiz.
           6k bit-mapped (0-paper, 1-pen).
            + 6k attribute file. Each attribute covers a byte
            slice. (8 pixels horiz.) Worked as above.

MODE 3.    Hi-resolution.
           192 pixels vert * 512 horiz.
           24k bit-mapped. 2 bits per pixel giving 4 colours.
           D2 and D3 for every colour is given by hmpr (see
            above).

MODE 4.    Start-up mode.
           192 pixels vert* 256 horiz.
           24k bit-mapped. 4 bits per pixel giving 16 colours.