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The +D system variables and tables 

THE 'SYSTEM VARIABLES'
These variables hold various settings for drives etc. The variables starting at address
#2000 can be accessed from BASIC with POKE @p,n. Where p is 0 for RBCC at #2000.

2000 RBCC       DEFB #07                 Flashing borders.
2001 TRAKS1     DEFB 80+128              Drive 1 80 tracks double sided.
2002 TRAKS2     DEFB 80+128              Drive 2 80 tracks double sided.
2003 STPRAT     DEFB 0                   "Steprate" 0 msec.
2004 NSTAT      DEFB 1                   Network on?
2005 WIDTH      DEFB 80                  Printer right margin.
2006 PCODE      DEFB 0                   Expand tokens, etc. before printing.
2007 LSPCE      DEFB 12                  Line spacing 12/72 inch.
2008 LFEED      DEFB 1                   Number of line feeds after CR 1.
2009 LMARG      DEFB 0                   Left margin at 0.
200A GRAPH      DEFB 0                   Print special graphics off.
200B ZXPNT      DEFB 0                   +D printer port on.
200C RESERVED   DEFW #0000
200E ONERR      DEFW #0000               Address of routine called after an
                                         error has occurred.
2010 EVERY_INT  DEFW #208F               Address of routine called at every
                                         interrupt.

THE 'PRINTER CODES' TABLE
Here the printer control codes are stored.

2012 INIT_PRT   DEFB 27,"@",#80,#80
2016            DEFB #80,#80,#80,#80
201A CHAR_PITCH DEFB #80,#80,#80,#80
201E            DEFB #80,#80,#80,#80
2022 N/72_LSPC  DEFB 27,"A",#80,#80
2026            DEFB #80,#80,#80,#80
202A GRAPH_DPI  DEFB 27,"*",5,#80
202E            DEFB #80,#80,#80,#80
2032 INIT_PRT2  DEFB #80,#80,#80,#80
2036            DEFB #80,#80,#80,#80

THE 'GRAPHIC REPRESENTATION' TABLE
This table consists of the graphic representations of the , # and  signs. The 'GRAPH'
system variable (@10) determines whether the normal code or the graphic representation is
outputted to the printer.

203A _SIGN     DEFB %00011000
203B            DEFB %00100000
203C            DEFB %00100000
203D            DEFB %01111000
203E            DEFB %00100000
203F            DEFB %00100000
2040            DEFB %01111100
2041            DEFB %00000000

2042 #_SIGN     DEFB %00000000
2043            DEFB %00100100
2044            DEFB %01111110
2045            DEFB %00100100
2046            DEFB %00100100
2047            DEFB %01111110
2048            DEFB %00100100
2049            DEFB %00000000

204A -SIGN     DEFB %01111110
204B            DEFB %10000001
204C            DEFB %10111101
204D            DEFB %10100001
204E            DEFB %10100001
204F            DEFB %10111101
2050            DEFB %10000001
2051            DEFB %01111110

THE 'GREYSCALE' PRINTER CONTROL CODE
This code is outputted to the printer if a 'SCREEN$ 2' screendump is wanted.

2052 GREY_BITIM DEFB 27,"*",5,#40
2056            DEFB #02,#80,#80,#80

THE 'GREYSCALE' TABLE
This table consists of three times three bytes of greyscale info. Each screen pixel is
converted into 3x3 printer dots during greyscale printing. The printer dots are ordered
as follows: The first dot row is produced from the first three bytes by taking the bit,
which number is corresponding with the colour number, from each of the three bytes. E.g.
for colour 2 (=red) bit 2 is used. In the same way the second and third dot rows are
produced from the second and third three bytes respectively.
The following eight 3x3 matrices are produced:

 White  Yellow  Cyan  Green Magenta  Red    Blue  Black
  000    000    100    000    100    010    110    111
  000    010    010    101    111    111    111    111
  000    000    001    000    001    010    011    111

Note that some greytones aren't right. E.g. cyan is darker than green, which isn't so on
the screen.

                       colour
                      76543210

205A GREYSCALE  DEFB %00101011
205B            DEFB %00011111           first row
205C            DEFB %00000001

205D            DEFB %00000111
205E            DEFB %01101111           second row
205F            DEFB %00000111

2060            DEFB %00000001
2061            DEFB %00011111           third row
2062            DEFB %00101011

2063            DEFW #1429,P_ALL         Address of 'output' routine for "P".
2065            DEFB #00                 The 'ENTER' flag.
2066            DEFW #0000               D_ERR_SP
2067            DEFB #00

THE 'SNAPSHOT-FILE' UFIA
The following bytes are the last 20 bytes of a snapshot file UFIA.

2068 SNAP_UFIA  DEFB 0                   Directory description.
2069            DEFM "Snap      "        File name.
2073            DEFB 3                   File type.
2074            DEFW #0000               File length.
2076            DEFW #0000               File address.
2078            DEFW #0000               Not used with Snap's.
207A            DEFW #FFFF               Not used with Snap's.

SOME 'LOST' ASSEMBLER TEXT
Miles-Gordon seem to have lost some of their assembler text.

207C            DEFM "JP"
207E            DEFB #07
207F            DEFB "Z"

THE 'RAM JUMPS'
These 13 'jumps' are used from the ROM to call +D System routines present in RAM (after
the System file has been loaded).

2080 JCOPS      NOP                      The small dump isn't patched.
2081            NOP
2082            RET
2083 JCOPS2     NOP                      Neither is the greyscale dump.
2084            NOP
2085            RET
2086 JPCHAN     NOP                      Nor the PCHAN_OUT routine.
2087            NOP
2088            RET
2089 JPOKE      NOP                      Nor the POKE routine.
208A            NOP
208B            RET
208C JPRTR      NOP                      Even the TAKE_PRTR routine isn't
208D            NOP                      patched.
208E            RET
208F JJIFFY     NOP                      Called EVERY_INT.
2090            NOP
2091            RET
2092 JLOAD      JP   #28EE,LD_VF_MR1     Load the file.
2095 JHXFER     JP   #2F8B,HXFER         Transfer UFIA to DFCA.
2098 JKSCAN     JP   #2245,JIFFY         Called every interrupt.
209B JMSG3      JP   #3090,MSG_3         Give the copyright message.
209E JHOOK      JP   #228E,HOOK_CODE     Execute the hook or command code.
20A1 JSNAP      JP   #2115,SNAP          Continue with the Snapshot routine.
20A4 JCTRL      JP   #20A7,CTRL          Continue with the control routine.

THE 'CONTROL ROUTINE' CONTINUED
The final part of the control routine determines which command failed the Spectrum
syntax. If it is a +D command then the apropriate routine is executed.

20A7 CTRL       PUSH AF
20A8            LD   HL,#3DF4
20AB            LD   BC,60
20AE RESET_VARS LD   (HL),255            Reset +D work areas, including UFIA1
20B0            INC  HL                  and UFIA2.
20B1            DEC  BC 20B2            LD   A,B
20B3            OR   C
20B4            JR   NZ,#20AE,RESET_VARS
20B6            LD   (#3ACF),A           Clear FLAGS3.
20B9            LD   IX,#3AC3            Point to +D system variables.
20BD            POP  AF                  Fetch the command.
20BE            LD   (#3DFF),A           Store it.
20C1            CP   207                 Is the command 'CAT' ?
20C3            JP   Z,#245B,CAT         Jump to the CAT routine if so.
20C6            CP   208                 Also for 'FORMAT',...
20C8            JP   Z,#2AB9,FORMAT
20CB            CP   209                 ...'MOVE',...
20CD            JP   Z,#2B03,MOVE
20D0            CP   210                 ...'ERASE',...
20D2            JP   Z,#250C,ERASE
20D5            CP   211                 ...'OPEN #',...
20D7            JP   Z,#2C68,OPEN
20DA            CP   212                 ...'CLOSE #',...
20DC            JP   Z,#2E16,CLOSE
20DF            CP   213                 ...'MERGE',...
20E1            JP   Z,#28E4,MERGE
20E4            CP   214                 ...'VERIFY',...
20E6            JP   Z,#28DF,VERIFY
20E9            CP   239                 ...'LOAD',...
20EB            JP   Z,#28DA,LOAD
20EE            CP   248                 ...'SAVE',...
20F0            JP   Z,#288B,SAVE
20F3            CP   251                 ...'CLS',...
20F5            JP   Z,#2EB9,CLS
20F8            CP   253                 ...'CLEAR',...
20FA            JP   Z,#2E39,CLEAR
20FD            CP   255                 ...'COPY',...
20FF            JP   Z,#3020,COPY
2102            LD   HL,(#200E)          Fetch ONERR address.
2105            LD   A,H
2106            OR   L
2107            RET  Z                   Return if no ON ERROR address.
2108            LD   (#2110),HL          Store it so it can be CALBASsed.
210B            POP  HL                  Drop return address.
210C            LD   A,(#3DFF)           Fetch command which has to be examined
210F            RST  #10,CALBAS          by user-routine (BASIC extensions).
2110            DEFW #0000               CALL the extend BASIC routine(s).
2112            JP   #047C,END           Test end of command and exit.

THE 'SNAPSHOT ROUTINE' CONTINUED
Here the snapshot routine continues with the disk related functions, keys 3-5.

2115 SNAP       LD   HL,16384            start of RAM (also start of SCR$).
2118            BIT  2,E
211A            JR   NZ,#2123,NO_SCR     3: Save SCREEN$.
211C            LD   A,7                 type=SCR$.
211E            LD   DE,6912             length of SCR$.
2121            JR   #2139,SNAP_SAVE

2123 NO_SCR     BIT  3,E
2125            JR   NZ,#212E,NO_SNP48   4: 48K Snapshot.
2127            LD   A,5                 type=48K Snap.
2129            LD   DE,49152            length of 48K RAM.
212C            JR   #2139,SNAP_SAVE

212E NO_SNP48   BIT  4,E
2130            RET  NZ                  Exit if not 5: 128K Snapshot.
2131            LD   A,9                 Type=128K Snap.
2133            LD   DE,16384            Length of a RAM-page.
2136            LD   HL,49152            Start of a RAM-page.
2139 SNAP_SAVE  LD   (#2068),A           Store type in snapshot UFIA.
213C            LD   (#2074),DE          Store length in UFIA.
2140            LD   (#2076),HL          And the start-address.
2143            POP  AF                  Drop return addres.
2144            LD   B,#FE               Key CAPS-V I/O address.
2146            IN   A,(C)
2148            BIT  0,A
214A            JR   NZ,#2154,SNAP_NAME  If CAPS is pressed the Snap goes to
214C            LD   A,(#3ACE)           the other drive.
214F            XOR  #03
2151            LD   (#3ACE),A
2154 SNAP_NAME  LD   A,%01000000
2156            CALL #09A5,SCAN_CAT      Search first free catalogue entry.
2159            RET  NZ                  Exit if catalogue full.
215A            LD   A,D                 Track to A.
215B            AND  #07                 Jump if CAT-entry will be located
215D            JR   Z,#2164,SNAP_N1     on track 0.

The name a snapshot-file is given, depends on the position it's going to occupy in the
directory. When the entry will be located on the first track the names range from 'Snap
A' to 'Snap T', if however the entry will be located on track 1 to 3 the character after
'Snap' will be the track number. I.e. 'Snap1A' to 'Snap1T' for track 1, etc. Notice that
the character after 'Snap' is never set to a ' '.

215F            ADD  A,48                ASCII offset for '0'.
2161            LD   (#206D),A           Store a 1, 2 or 3 in name-part of UFIA.
2164 SNAP_N1    LD   L,E                 Store sector in L.
2165            SLA  L                   Two entries per sector.
2167            DEC  L
2168            LD   A,(IX+14)           Is it the first or second entry in the
216B            ADD  A,L                 CAT-sector.
216C            ADD  A,64                Add ASCII 'A' offset.
216E            LD   (#206E),A           Store 'A' to 'T' in name-part of UFIA.
2171            LD   HL,#2068,SNAP_UFIA  Copy UFIA to DFCA.
2174            LD   DE,#3E05
2177            LD   BC,20
217A            LDIR
217C            CALL #0AD9,OFSM_2        Open the file.
217F            LD   HL,#3FEA            Copy snap registers to catalogue entry.
2182            LD   DE,#3BB2
2185            LD   BC,22
2188            LDIR
218A            LD   A,(#2068)           Get directory description.
218D            CP   9
218F            JP   NZ,#222D,NO_SNP128  Jump if not a 128K Snapshot.
2192            LD   HL,49152            Now the 5 first bytes of the current
2195            LD   DE,#3BD6            RAM-page are saved in the +D RAM
2198            LD   BC,5                and replaced by the "BRUCE" message.
219B            LDIR                     This is done to determine the currently
219D            LD   HL,#2228,BRUCE      paged in RAM-page.
21A0            LD   DE,49152
21A3            LD   BC,5
21A6            LDIR
21A8            XOR  A                   Signal '128K ROM bank active'.
21A9            LD   (#3E19),A
21AC            CALL #011D,?_ROMBANK     Determine current 'main' ROM bank.
21AF            JR   NZ,#21B6,SNP128_1   Jump if 128K ROM bank.
21B1            LD   A,#10               Signal '48K ROM bank active'.
21B3            LD   (#3E19),A
21B6 SNP128_1   CALL #0511,REST_PBUF     Restore printer buffer contents.
21B9            LD   A,(#3E19)
21BC            CALL #223F,RAMPAGE_A     Page in current ROM bank & RAM page 0.

The code now tests which screen is active. Because it isn't possible to detect which is
the active screen, the user is consulted. By making nice border stripes the user is
signalled that 'Y' (meaning: yes, screen changed) or 'N' (meaning: no, screen hasn't
changed) has to be pressed.

21BF SNP128_2   LD   BC,#DFFE            Keyboard port and I/O address for Y-P.
21C2            IN   E,(C)
21C4            BIT  4,E
21C6            JR   Z,#21D7,CHANGED_$   Jump if 'Y' was pressed, screen changed
21C8            LD   B,#7F               I/O address for B-SPACE.
21CA            IN   E,(C)
21CC            BIT  3,E
21CE            JR   Z,#21E2,SAME_$      Jump if 'N' was pressed, same screen.
21D0            INC  A
21D1            AND  #07
21D3            OUT  (C),A               Make nice stripes in border again.
21D5            JR   #21BF,SNP128_2      Only 'Y' or 'N' is accepted.

21D7 CHANGED_$  LD   A,(#3E19)
21DA            OR   #08                 Signal 'screen 1'.
21DC ?_RAMBANK  LD   (#3E19),A
21DF            CALL #223F,RAMPAGE_A     Page in active ROM bank and screen.

Now the 'which RAM bank' test is executed. The active RAM bank is determined by
searching which bank has been given the "BRUCE" message.

21E2 SAME_$     LD   DE,49152            Here the message has been placed.
21E5            LD   HL,#2228,BRUCE      Message to be found.
21E8            LD   B,5                 There are five bytes in the message.
21EA BRUCE_1    LD   A,(DE)
21EB            CP   (HL)
21EC            JR   Z,#21F4,BRUCE_2     Jump if characters match.
21EE            LD   A,(#3E19)           Otherwise it has to be one of the other
21F1            INC  A                   banks.
21F2            JR   ?_RAMBANK

21F4 BRUCE_2    INC  DE
21F5            INC  HL
21F6            DJNZ #21EA,BRUCE_1       All five characters have to match.
21F8            LD   HL,#3BD6            The active RAM bank has been found,
21FB            LD   DE,49152            restore the original five bytes.
21FE            LD   BC,5
2201            LDIR
2203            LD   A,(#3E19)
2206            PUSH AF                  Save the page-configuration byte in the
2207            CALL #0761,SBYT          snapshot file.
220A            AND  #F8                 Mask RAM bank, start with 0.
220C            LD   B,8                 There are eight RAM banks
220E SAVE_BANK  PUSH AF
220F            PUSH BC
2210            CALL #223F,RAMPAGE_A     Page in RAM bank.
2213            LD   HL,(#2076)
2216            LD   DE,(#2074)
221A            CALL #0850,HSVBK_2       Save DE bytes starting at address HL.
221D            POP  BC
221E            POP  AF
221F            INC  A                   Next RAM bank.
2220            DJNZ #220E,SAVE_BANK     Loop for all eight 16K RAM banks.
2222            POP  AF
2223            CALL #223F,RAMPAGE_A     Page in original RAM bank.
2226            JR   #223C,SNAP_CLOSE

2228 BRUCE      DEFM "BRUCE"

222D NO_SNP128  CP   7                   Copy the 9 header bytes to the file if
222F            CALL Z,#2879,SAVE_HEAD1  it is a SCREEN$.
2232            LD   HL,(#2076)
2235            LD   DE,(#2074)
2239            CALL #0850,HSVBK_2       Save DE bytes starting at address HL.
223C SNAP_CLOSE JP   #0B89,CFSM          Close the file.

THE 'PAGE 128K RAM' ROUTINE
The 128K RAM-bank contained in the A register is paged-in.

223F RAMPAGE_A  LD   BC,#7FFD            128K bank-switch port address.
2242            OUT  (C),A               Select RAM bank.
2244            RET

THE 'JIFFY' CALL
This routine is executed whenever KEY-SCAN in the Spectrum ROM is reached at #028E. It
can be used to executed a routine with every interrupt.

2245 JIFFY      LD   HL,(#2010)          Call routine which has to be called
2248            JP   (HL)                every 'interrupt'. (Normal #208F)


THE 'MOUSE' ROUTINE
This routine is also present in the DISCiPLE and tests a mouse-like device. Pointers
which seem to keep track of screen coordinates are updated when necessary.

2249 TEST_MOUSE LD   BC,#03FF            The MGT mouse port?
224C            IN   A,(C)
224E            BIT  7,A
2250            RET  NZ                  Return if no activity.
2251            CPL
2252            AND  #05                 Return if there was no horizontal or
2254            RET  Z                   vertical movement.
2255            LD   HL,#228B,SIGN_MOUSE
2258            PUSH HL
2259            LD   HL,#2275,MOVE_VERT
225C            PUSH HL
225D            IN   D,(C)               Read mouse bits again.
225F            LD   HL,#3DF1            Mouses x-coordinate.
2262            BIT  0,D
2264            RET  NZ                  Return to vertical movement test.
2265            BIT  1,D
2267            JR   Z,#226F,MOVE_RIGHT  Jump if mouse was moved right.
2269            LD   A,0                 Left side of screen.
226B            CP   (HL)
226C            RET  Z                   Return if left movement isn't possible.
226D            DEC  (HL)                Otherwise decrement x-coordinate.
226E            RET

226F MOVE_RIGHT LD   A,255               Right side of screen.
2271            CP   (HL)
2272            RET  Z                   Return if right movement impossible.
2273            INC  (HL)                Otherwise increment x.
2274            RET

2275 MOVE_VERT  LD   HL,#3DF2            Y-coordinate of mouse.
2278            BIT  2,D
227A            RET  NZ                  Return to signal mouse.
227B            BIT  3,D
227D            JR   NZ,#2285,MOVE_UP    Jump if mouse was moved up.
227F            LD   A,0                 Bottom side of screen.
2281            CP   (HL)
2282            RET  Z                   Return if bottom has been reached.
2283            DEC  (HL)                Otherwise move towards it.
2284            RET

2285 MOVE_UP    LD   A,175               Top side of screen.
2287            CP   (HL)
2288            RET  Z                   Return if top was reached.
2289            INC  (HL)                Otherwise increment y-coordinate.
228A            RET

228B SIGN_MOUSE OUT  (C),D               Give original signal to mouse.
228D            RET

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