Skip to navigation

⌂ ∞ ▽ Elite on the 6502

Version analysis of TT102

This code appears in the following versions (click to see it in the source code):

Code variations between these versions are shown below.

       Name: TT102
       Type: Subroutine
   Category: Keyboard
    Summary: Process function key, save key, hyperspace and chart key presses

Code variation 1 of 29A variation in the comments only

This variation is blank in the Disc (docked) version.

Cassette, Flight, 6502SP, Master, Electron
             and update the hyperspace counter




 Process function key presses, plus "@" (save commander), "H" (hyperspace),
 "D" (show distance to system) and "O" (move chart cursor back to current
 system). We can also pass cursor position deltas in X and Y to indicate that

Code variation 2 of 29A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Master
Electron
 the cursor keys or joystick have been used (i.e. the values that are returned
 by routine TT17).

 the cursor keys have been used (i.e. the values that are returned by routine
 TT17).

Code variation 3 of 29A variation in the comments only

This variation is blank in the Cassette, Disc (flight) and Electron versions.

Docked, 6502SP, Master
 This routine also checks for the "F" key press (search for a system), which
 applies to enhanced versions only.




 Arguments:

Code variation 4 of 29A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Master
Electron
   A                    The internal key number of the key pressed (see p.142 of
                        the Advanced User Guide for a list of internal key
                        numbers)

   A                    The internal key number of the key pressed (see p.40 of
                        the Electron Advanced User Guide for a list of internal
                        key numbers)


   X                    The amount to move the crosshairs in the x-axis

   Y                    The amount to move the crosshairs in the y-axis



 Other entry points:

   T95                  Print the distance to the selected system

Code variation 5 of 29Specific to an individual platform

This variation is blank in the Cassette, Disc (flight), Disc (docked), 6502 Second Processor and Master versions.

Electron
.VKEYS

 EQUB func2             \ The key to press for showing view 1 (back)

 EQUB func3             \ The key to press for showing view 2 (left)

 EQUB func4             \ The key to press for showing view 3 (right)

.TT102

Code variation 6 of 29A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Master
Electron
 CMP #f8                \ If red key f8 was pressed, jump to STATUS to show the
 BNE P%+5               \ Status Mode screen, returning from the subroutine
 JMP STATUS             \ using a tail call

 CMP #f4                \ If red key f4 was pressed, jump to TT22 to show the
 BNE P%+5               \ Long-range Chart, returning from the subroutine using
 JMP TT22               \ a tail call

 CMP #f5                \ If red key f5 was pressed, jump to TT23 to show the
 BNE P%+5               \ Short-range Chart, returning from the subroutine using
 JMP TT23               \ a tail call

 CMP #func9             \ If FUNC-9 was pressed, jump to STATUS to show the
 BNE P%+5               \ Status Mode screen, returning from the subroutine
 JMP STATUS             \ using a tail call

 CMP #func5             \ If FUNC-5 was pressed, jump to TT22 to show the
 BNE P%+5               \ Long-range Chart, returning from the subroutine using
 JMP TT22               \ a tail call

 CMP #func6             \ If FUNC-6 was pressed, jump to TT23 to show the
 BNE P%+5               \ Short-range Chart, returning from the subroutine using
 JMP TT23               \ a tail call

Code variation 7 of 29A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette
Flight, Docked, 6502SP, Master
Electron
 CMP #f6                \ If red key f6 was pressed, call TT111 to select the
 BNE TT92               \ system nearest to galactic coordinates (QQ9, QQ10)
 JSR TT111              \ (the location of the chart crosshairs) and jump to
 JMP TT25               \ TT25 to show the Data on System screen, returning
                        \ from the subroutine using a tail call

 CMP #f6                \ If red key f6 was pressed, call TT111 to select the
 BNE TT92               \ system nearest to galactic coordinates (QQ9, QQ10)
 JSR TT111              \ (the location of the chart crosshairs) and set ZZ to
 JMP TT25               \ the system number, and then jump to TT25 to show the
                        \ Data on System screen (along with an extended system
                        \ description for the system in ZZ if we're docked),
                        \ returning from the subroutine using a tail call

 CMP #func7             \ If FUNC-7 was pressed, call TT111 to select the
 BNE TT92               \ system nearest to galactic coordinates (QQ9, QQ10)
 JSR TT111              \ (the location of the chart crosshairs) and jump to
 JMP TT25               \ TT25 to show the Data on System screen, returning
                        \ from the subroutine using a tail call

.TT92

Code variation 8 of 29A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Master
Electron
 CMP #f9                \ If red key f9 was pressed, jump to TT213 to show the
 BNE P%+5               \ Inventory screen, returning from the subroutine
 JMP TT213              \ using a tail call

 CMP #f7                \ If red key f7 was pressed, jump to TT167 to show the
 BNE P%+5               \ Market Price screen, returning from the subroutine
 JMP TT167              \ using a tail call

 CMP #func0             \ If FUNC-0 was pressed, jump to TT213 to show the
 BNE P%+5               \ Inventory screen, returning from the subroutine
 JMP TT213              \ using a tail call

 CMP #func8             \ If FUNC-8 was pressed, jump to TT167 to show the
 BNE P%+5               \ Market Price screen, returning from the subroutine
 JMP TT167              \ using a tail call

Code variation 9 of 29A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP
Master
Electron
 CMP #f0                \ If red key f0 was pressed, jump to TT110 to launch our
 BNE fvw                \ ship (if docked), returning from the subroutine using
 JMP TT110              \ a tail call

 CMP #f0                \ If red key f0 was pressed, jump to TT110 to launch our
 BNE fvw                \ ship (if docked), returning from the subroutine using
\JSR CTRL               \ a tail call
\BPL P%+5               \
\JMP HALL               \ Three instructions are commented out in the original
 JMP TT110              \ source, which would show the ship hangar instead of
                        \ launching if CTRL is held down, so presumably they
                        \ were put in for testing

 CMP #func1             \ If FUNC-1 was pressed, jump to TT110 to launch our
 BNE fvw                \ ship (if docked), returning from the subroutine using
 JMP TT110              \ a tail call

.fvw

Code variation 10 of 29Specific to an individual platform

This variation is blank in the Disc (flight) and Disc (docked) versions.

Tap on a block to expand it, and tap it again to revert.

Cassette, 6502SP, Master
Electron
 BIT QQ12               \ If bit 7 of QQ12 is clear (i.e. we are not docked, but
 BPL INSP               \ in space), jump to INSP to skip the following checks
                        \ for f1-f3 and "@" (save commander file) key presses

 BIT QQ12               \ If bit 7 of QQ12 is clear (i.e. we are not docked, but
 BPL INSP               \ in space), jump to INSP to skip the following checks
                        \ for FUNC-2 to FUNC-4 and "@" (save commander file) key
                        \ presses

Code variation 11 of 29Specific to an individual platform

This variation is blank in the Disc (flight) version.

Tap on a block to expand it, and tap it again to revert.

Cassette, Docked, 6502SP, Master
Electron
 CMP #f3                \ If red key f3 was pressed, jump to EQSHP to show the
 BNE P%+5               \ Equip Ship screen, returning from the subroutine using
 JMP EQSHP              \ a tail call

 CMP #f1                \ If red key f1 was pressed, jump to TT219 to show the
 BNE P%+5               \ Buy Cargo screen, returning from the subroutine using
 JMP TT219              \ a tail call

 CMP #func4             \ If FUNC-4 was pressed, jump to EQSHP to show the
 BNE P%+5               \ Equip Ship screen, returning from the subroutine using
 JMP EQSHP              \ a tail call

 CMP #func2             \ If FUNC-2 was pressed, jump to TT219 to show the
 BNE P%+5               \ Buy Cargo screen, returning from the subroutine using
 JMP TT219              \ a tail call

Code variation 12 of 29Related to an enhanced feature

Pressing "@" brings up the disc access menu in the enhanced versions.

See below for more variations related to this code.

This variation is blank in the Disc (flight) version.

Tap on a block to expand it, and tap it again to revert.

Cassette
Docked, 6502SP
Master
Electron
 CMP #&47               \ If "@" was pressed, jump to SVE to save the commander
 BNE P%+5               \ file, returning from the subroutine using a tail call
 JMP SVE

 CMP #&47               \ If "@" was not pressed, skip to nosave
 BNE nosave

 CMP #'@'               \ If "@" was not pressed, skip to nosave
 BNE nosave

 CMP #&48               \ If "@" was pressed, jump to SVE to save the commander
 BNE P%+5               \ file, returning from the subroutine using a tail call
 JMP SVE

Code variation 13 of 29Related to an enhanced feature

See variation 12 above for details.

This variation is blank in the Cassette, Disc (flight) and Electron versions.

Docked, 6502SP, Master
 JSR SVE                \ "@" was pressed, so call SVE to show the disc access
                        \ menu

 BCC P%+5               \ If the C flag was set by SVE, then we loaded a new
 JMP QU5                \ commander file, so jump to QU5 to restart the game
                        \ with the newly loaded commander

 JMP BAY                \ Otherwise the C flag was clear, so jump to BAY to go
                        \ to the docking bay (i.e. show the Status Mode screen)

.nosave

Code variation 14 of 29Specific to an individual platform

This variation is blank in the Disc (flight) version.

Tap on a block to expand it, and tap it again to revert.

Cassette, Docked, 6502SP, Master
Electron
 CMP #f2                \ If red key f2 was pressed, jump to TT208 to show the
 BNE LABEL_3            \ Sell Cargo screen, returning from the subroutine using
 JMP TT208              \ a tail call

.INSP

 CMP #func3             \ If FUNC-3 was pressed, jump to TT208 to show the Sell
 BNE LABEL_3            \ Cargo screen, returning from the subroutine using a
 JMP TT208              \ tail call

.INSP

Code variation 15 of 29Specific to an individual platform

This variation is blank in the Disc (docked) version.

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, 6502SP
Master
Electron
 CMP #f1                \ If the key pressed is < red key f1 or > red key f3,
 BCC LABEL_3            \ jump to LABEL_3 (so only do the following if the key
 CMP #f3+1              \ pressed is f1, f2 or f3)
 BCS LABEL_3

 AND #3                 \ If we get here then we are either in space, or we are
 TAX                    \ docked and none of f1-f3 were pressed, so we can now
 JMP LOOK1              \ process f1-f3 with their in-flight functions, i.e.
                        \ switching space views
                        \
                        \ A will contain &71, &72 or &73 (for f1, f2 or f3), so
                        \ set X to the last digit (1, 2 or 3) and jump to LOOK1
                        \ to switch to view X (rear, left or right), returning
                        \ from the subroutine using a tail call

 CMP #f1                \ If red key f1 was pressed, jump to chview1
 BEQ chview1

 CMP #f2                \ If red key f2 was pressed, jump to chview2
 BEQ chview2

 CMP #f3                \ If red key f3 was not pressed, jump to LABEL_3 to keep
 BNE LABEL_3            \ checking for which key was pressed

 LDX #3                 \ Red key f3 was pressed, so set the view number in X to
                        \ 3 for the right view

 EQUB &2C               \ Skip the next instruction by turning it into
                        \ &2C &A2 &02, or BIT &02A2, which does nothing apart
                        \ from affect the flags

.chview2

 LDX #2                 \ If we jump to here, red key f2 was pressed, so set the
                        \ view number in X to 2 for the left view

 EQUB &2C               \ Skip the next instruction by turning it into
                        \ &2C &A2 &01, or BIT &02A2, which does nothing apart
                        \ from affect the flags

.chview1

 LDX #1                 \ If we jump to here, red key f1 was pressed, so set the
                        \ view number in X to 1 for the rear view

 JMP LOOK1              \ Jump to LOOK1 to switch to view X (rear, left or
                        \ right), returning from the subroutine using a tail
                        \ call

 STX T                  \ Store X in T so we can retrieve it after the following

 LDX #3                 \ We are about to loop through the key presses for the
                        \ four views, so set a counter in X, starting with a
                        \ value of X = 3 (for the right view)

.LOOKL

 CMP VKEYS-1,X          \ If the key pressed does not match the value in VKEYS
 BNE P%+5               \ for view X, skip the following instruction

 JMP LOOK1              \ The key pressed matches the key in position X, so jump
                        \ to LOOK1 to switch to view X (rear, left or right),
                        \ returning from the subroutine using a tail call

 DEX                    \ Decrement the view number in X, so we start with view
                        \ 3 (right), then work backwards through 2 (left) and
                        \ 1 (rear)

 BNE LOOKL              \ Loop back to check the next key until we have checked
                        \ for f3, f2 and f1

 LDX T                  \ Fetch the value of X that we stored in T above

.LABEL_3

Code variation 16 of 29A variation in the labels only

This variation is blank in the Cassette, Disc (flight), Disc (docked), Master and Electron versions.

6502SP
                        \ In the 6502 Second Processor version, the LABEL_3
                        \ label is actually `` (two backticks), but that doesn't
                        \ compile in BeebAsm and it's pretty cryptic, so instead
                        \ this version sticks with the label LABEL_3 from the
                        \ cassette version

Code variation 17 of 29Specific to an individual platform

When docked in the disc version, the screen-clearing and DOCKED printing is done here rather than in hyp and hy6, but the code is the same.

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, 6502SP, Electron
Docked
Master
 CMP #&54               \ If "H" was pressed, jump to hyp to do a hyperspace
 BNE P%+5               \ jump (if we are in space), returning from the
 JMP hyp                \ subroutine using a tail call

 CMP #&54               \ If "H" was not pressed, jump to NWDAV5 to skip the
 BNE NWDAV5             \ following

 JSR CLYNS              \ "H" was pressed, so clear the bottom three text rows
                        \ of the upper screen, and move the text cursor to
                        \ column 1 on row 21, i.e. the start of the top row of
                        \ the three bottom rows

 LDA #15                \ Move the text cursor to column 15 (the middle of the
 STA XC                 \ screen)

 LDA #205               \ Print extended token 205 ("DOCKED") and return from
 JMP DETOK              \ the subroutine using a tail call

 LDA KL                 \ If "H" was not pressed, jump to NWDAV5 to skip the
 CMP #'H'               \ following
 BNE NWDAV5

 JMP hyp                \ Jump to hyp to do a hyperspace jump (if we are in
                        \ space), returning from the subroutine using a tail
                        \ call

Code variation 18 of 29A variation in the labels only

This variation is blank in the Cassette, Disc (flight) and Electron versions.

Docked, 6502SP, Master
.NWDAV5

Code variation 19 of 29Specific to an individual platform

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Electron
Master
 CMP #&32               \ If "D" was pressed, jump to T95 to print the distance
 BEQ T95                \ to a system (if we are in one of the chart screens)

 CMP #'D'               \ If "D" was pressed, jump to T95 to print the distance
 BEQ T95                \ to a system (if we are in one of the chart screens)

Code variation 20 of 29Related to an enhanced feature

Pressing "F" in the enhanced versions when viewing a chart lets us search for systems by name.

See below for more variations related to this code.

This variation is blank in the Cassette, Disc (flight) and Electron versions.

Tap on a block to expand it, and tap it again to revert.

Docked, 6502SP
Master
 CMP #&43               \ If "F" was not pressed, jump down to HME1, otherwise
 BNE HME1               \ keep going to process searching for systems

 CMP #'F'               \ If "F" was not pressed, jump down to HME1, otherwise
 BNE HME1               \ keep going to process searching for systems

Code variation 21 of 29Specific to an individual platform

This variation is blank in the Cassette, Disc (flight), Disc (docked) and Electron versions.

6502SP, Master
 LDA QQ12               \ If QQ12 = 0 (we are not docked), we can't search for
 BEQ t95                \ systems, so return from the subroutine (as t95
                        \ contains an RTS)

Code variation 22 of 29Related to an enhanced feature

See variation 20 above for details.

This variation is blank in the Cassette, Disc (flight) and Electron versions.

Docked, 6502SP, Master
 LDA QQ11               \ If the current view is a chart (QQ11 = 64 or 128),
 AND #%11000000         \ keep going, otherwise return from the subroutine (as
 BEQ t95                \ t95 contains an RTS)

 JMP HME2               \ Jump to HME2 to let us search for a system, returning
                        \ from the subroutine using a tail call

.HME1

 STA T1                 \ Store A (the key that's been pressed) in T1

Code variation 23 of 29Specific to an individual platform

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, 6502SP, Master, Electron
Docked
 LDA QQ11               \ If the current view is a chart (QQ11 = 64 or 128),
 AND #%11000000         \ keep going, otherwise jump down to TT107 to skip the
 BEQ TT107              \ following

 LDA QQ22+1             \ If the on-screen hyperspace counter is non-zero,
 BNE TT107              \ then we are already counting down, so jump to TT107
                        \ to skip the following

 LDA QQ11               \ If the current view is a chart (QQ11 = 64 or 128),
 AND #%11000000         \ keep going, otherwise jump down to t95 to return from
 BEQ t95                \ the subroutine

 LDA QQ22+1             \ If the on-screen hyperspace counter is non-zero,
 BNE t95                \ then we are already counting down, so jump down to t95
                        \ to return from the subroutine

 LDA T1                 \ Restore the original value of A (the key that's been
                        \ pressed) from T1

Code variation 24 of 29Specific to an individual platform

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Electron
Master
 CMP #&36               \ If "O" was pressed, do the following three jumps,
 BNE ee2                \ otherwise skip to ee2 to continue

 CMP #'O'               \ If "O" was pressed, do the following three jumps,
 BNE ee2                \ otherwise skip to ee2 to continue

 JSR TT103              \ Draw small crosshairs at coordinates (QQ9, QQ10),
                        \ which will erase the crosshairs currently there

 JSR ping               \ Set the target system to the current system (which
                        \ will move the location in (QQ9, QQ10) to the current
                        \ home system

Code variation 25 of 29Other (e.g. bug fix, optimisation)

This might be a bug fix? If "O" is pressed in the advanced versions, then the target system is set to home, and the routine terminates, which is different to the other versions; they stick around for one more move of the cursor, so presumably this fixes a bug where pressing "O" might not always move the cursor exactly to the current system.

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, Electron
6502SP, Master
 JSR TT103              \ Draw small crosshairs at coordinates (QQ9, QQ10),
                        \ which will draw the crosshairs at our current home
                        \ system

 JMP TT103              \ Draw small crosshairs at coordinates (QQ9, QQ10),
                        \ which will draw the crosshairs at our current home
                        \ system, and return from the subroutine using a tail
                        \ call

.ee2

 JSR TT16               \ Call TT16 to move the crosshairs by the amount in X
                        \ and Y, which were passed to this subroutine as
                        \ arguments

Code variation 26 of 29Specific to an individual platform

This variation is blank in the Disc (docked) version.

Cassette, Flight, 6502SP, Master, Electron
.TT107

 LDA QQ22+1             \ If the on-screen hyperspace counter is zero, return
 BEQ t95                \ from the subroutine (as t95 contains an RTS), as we
                        \ are not currently counting down to a hyperspace jump

 DEC QQ22               \ Decrement the internal hyperspace counter

 BNE t95                \ If the internal hyperspace counter is still non-zero,
                        \ then we are still counting down, so return from the
                        \ subroutine (as t95 contains an RTS)

                        \ If we get here then the internal hyperspace counter
                        \ has just reached zero and it wasn't zero before, so
                        \ we need to reduce the on-screen counter and update
                        \ the screen. We do this by first printing the next
                        \ number in the countdown sequence, and then printing
                        \ the old number, which will erase the old number
                        \ and display the new one because printing uses EOR
                        \ logic

 LDX QQ22+1             \ Set X = the on-screen hyperspace counter - 1
 DEX                    \ (i.e. the next number in the sequence)

 JSR ee3                \ Print the 8-bit number in X at text location (0, 1)

 LDA #5                 \ Reset the internal hyperspace counter to 5
 STA QQ22

 LDX QQ22+1             \ Set X = the on-screen hyperspace counter (i.e. the
                        \ current number in the sequence, which is already
                        \ shown on-screen)

 JSR ee3                \ Print the 8-bit number in X at text location (0, 1),
                        \ i.e. print the hyperspace countdown in the top-left
                        \ corner

 DEC QQ22+1             \ Decrement the on-screen hyperspace countdown

 BNE t95                \ If the countdown is not yet at zero, return from the
                        \ subroutine (as t95 contains an RTS)

 JMP TT18               \ Otherwise the countdown has finished, so jump to TT18
                        \ to do a hyperspace jump, returning from the subroutine
                        \ using a tail call

.t95

 RTS                    \ Return from the subroutine

.T95

                        \ If we get here, "D" was pressed, so we need to show
                        \ the distance to the selected system (if we are in a
                        \ chart view)

 LDA QQ11               \ If the current view is a chart (QQ11 = 64 or 128),
 AND #%11000000         \ keep going, otherwise return from the subroutine (as
 BEQ t95                \ t95 contains an RTS)

Code variation 27 of 29Related to the screen mode

This variation is blank in the Cassette, Disc (flight), Disc (docked), Master and Electron versions.

6502SP
 LDA #CYAN              \ Send a #SETCOL CYAN command to the I/O processor to
 JSR DOCOL              \ switch to colour 3, which is white in the chart view

 JSR hm                 \ Call hm to move the crosshairs to the target system
                        \ in (QQ9, QQ10), returning with A = 0

Code variation 28 of 29Specific to an individual platform

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Electron
Master
 STA QQ17               \ Set QQ17 = 0 to switch to ALL CAPS

\STA QQ17               \ This instruction is commented out in the original
                        \ source

 JSR cpl                \ Print control code 3 (the selected system name)

 LDA #%10000000         \ Set bit 7 of QQ17 to switch to Sentence Case, with the
 STA QQ17               \ next letter in capitals

Code variation 29 of 29Related to Elite's use of the Tube

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, Electron
Master
6502SP
 LDA #1                 \ Move the text cursor to column 1 and down one line
 STA XC                 \ (in other words, to the start of the next line)
 INC YC

 LDA #12                \ Print a line feed to move the text cursor down a line
 JSR TT26

 LDA #10                \ Print a line feed to move the text cursor down a line
 JSR TT26

 LDA #1                 \ Move the text cursor to column 1
 JSR DOXC

 JSR INCYC              \ Move the text cursor down one line

 JMP TT146              \ Print the distance to the selected system and return
                        \ from the subroutine using a tail call