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Elite on the BBC Micro

Version analysis of CLYNS

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

Code variations between these versions are shown below.

Name: CLYNS Type: Subroutine Category: Utility routines

Code variation 1 of 13A variation in the comments only

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Flight, Docked, Master, Electron

6502SP

Summary: Clear the bottom three text rows of the mode 4 screen
Summary: Implement the #clyns command (clear the bottom of the screen)

Code variation 2 of 13A variation in the comments only

This variation is blank in the 6502 Second Processor and Master versions.

Cassette, Flight, Docked, Electron

This routine clears some space at the bottom of the screen and moves the text cursor to column 1, row 21.

Code variation 3 of 13A variation in the comments only

This variation is blank in the 6502 Second Processor and Master versions.

Cassette, Flight, Docked, Electron

Specifically, it zeroes the following screen locations: &7507 to &75F0 &7607 to &76F0 &7707 to &77F0 which clears the three bottom text rows of the mode 4 screen (rows 21 to 23), clearing each row from text column 1 to 30 (so it doesn't overwrite the box border in columns 0 and 32, or the last usable column in column 31). Returns: A A is set to 0 Y Y is set to 0
.CLYNS

Code variation 4 of 13Specific to an individual platform

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

Master

STZ DLY \ Set the delay in DLY to 0, to indicate that we are \ no longer showing an in-flight message, so any new \ in-flight messages will be shown instantly STZ de \ Clear de, the flag that appends " DESTROYED" to the \ end of the next text token, so that it doesn't

Code variation 5 of 13Specific to an individual platform

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

Docked, Master

LDA #%11111111 \ Set DTW2 = %11111111 to denote that we are not STA DTW2 \ currently printing a word

Code variation 6 of 13Specific to an individual platform

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

Master

LDA #%10000000 \ Set bit 7 of QQ17 to switch standard tokens to STA QQ17 \ Sentence Case

Code variation 7 of 13Specific to an individual platform

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

Electron

JSR BORDER \ Redraw the space view's border, which removes it \ from the screen LDX #&71 \ Call LYN with X = &71 to clear the screen from page JSR LYN \ &71 to page &75, which clears the bottom three lines \ of the screen JSR BORDER \ Redraw the space view's border
 LDA #20                \ Move the text cursor to row 20, near the bottom of
 STA YC                 \ the screen

Code variation 8 of 13Related to the screen mode

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Flight

Docked

Master

6502SP

Electron

LDA #&75 \ Set the two-byte value in SC to &7507 STA SC+1 LDA #7 STA SC JSR TT67 \ Print a newline, which will move the text cursor down \ a line (to row 21) and back to column 1
JSR TT67 \ Print a newline, which will move the text cursor down \ a line (to row 21) and back to column 1 LDA #&75 \ Set the two-byte value in SC to &7507 STA SC+1 LDA #7 STA SC
JSR TT67_DUPLICATE \ Print a newline LDA #%00001111 \ Set bits 1 and 2 of the Access Control Register at STA VIA+&34 \ SHEILA &34 to switch screen memory into &3000-&7FFF LDA #&6A \ Set SC+1 = &6A, for the high byte of SC(1 0) STA SC+1 LDA #0 \ Set SC = 0, so now SC(1 0) = &6A00 STA SC
LDA #&6A \ Set SC+1 = &6A, for the high byte of SC(1 0) STA SC+1 JSR TT67 \ Print a newline LDA #0 \ Set SC = 0, so now SC(1 0) = &6A00 STA SC
JSR TT67 \ Print a newline, which will move the text cursor down \ a line (to row 21) and back to column 1

Code variation 9 of 13Related to the screen mode

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Docked

Flight

6502SP, Master

Electron

LDA #0 \ Call LYN to clear the pixels from &7507 to &75F0 JSR LYN INC SC+1 \ Increment SC+1 so SC points to &7607 JSR LYN \ Call LYN to clear the pixels from &7607 to &76F0 INC SC+1 \ Increment SC+1 so SC points to &7707 INY \ Move the text cursor to column 1 (as LYN sets Y to 0) STY XC \ Fall through into LYN to clear the pixels from &7707 \ to &77F0
LDA #0 \ Call LYN to clear the pixels from &7507 to &75F0 JSR LYN INC SC+1 \ Increment SC+1 so SC points to &7607 INY \ Move the text cursor to column 1 (as LYN sets Y to 0) STY XC \ Fall through into LYN to clear the pixels from &7707 \ to &77F0
LDX #3 \ We want to clear three text rows, so set a counter in \ X for 3 rows .CLYL LDY #8 \ We want to clear each text row, starting from the \ left, but we don't want to overwrite the border, so we \ start from the second character block, which is byte \ #8 from the edge, so set Y to 8 to act as the byte \ counter within the row .EE2 STA (SC),Y \ Zero the Y-th byte from SC(1 0), which clears it by \ setting it to colour 0, black INY \ Increment the byte counter in Y BNE EE2 \ Loop back to EE2 to blank the next byte along, until \ we have done one page's worth (from byte #8 to #255) INC SC+1 \ We have just finished the first page - which covers \ the left half of the text row - so we increment SC+1 \ so SC(1 0) points to the start of the next page, or \ the start of the right half of the row STA (SC),Y \ Clear the byte at SC(1 0), as that won't be caught by \ the next loop LDY #247 \ The second page covers the right half of the text row, \ and as before we don't want to overwrite the border, \ which we can do by starting from the last-but-one \ character block and working our way left towards the \ centre of the row. The last-but-one character block \ ends at byte 247 (that's 255 - 8, as each character \ is 8 bytes), so we put this in Y to act as a byte \ counter, as before
LDY #1 \ Move the text cursor to column 1 STY XC DEY \ Set Y = 0, so the subroutine returns with this value TYA .SC5 RTS \ Return from the subroutine

Code variation 10 of 13Specific to an individual platform

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

Tap on a version to expand it, and tap it again to show to all variations.

Master

6502SP

{ .EE3 \ This label is a duplicate of a label in TT23 (which is \ why we need to surround it with braces, as BeebAsm \ doesn't allow us to redefine labels, unlike BBC \ BASIC) STA (SC),Y \ Zero the Y-th byte from SC(1 0), which clears it by \ setting it to colour 0, black DEY \ Decrement the byte counter in Y BNE EE3 \ Loop back to EE2 to blank the next byte to the left, \ until we have done one page's worth (from byte #247 to \ #1) }
.EE3 STA (SC),Y \ Zero the Y-th byte from SC(1 0), which clears it by \ setting it to colour 0, black DEY \ Decrement the byte counter in Y BNE EE3 \ Loop back to EE2 to blank the next byte to the left, \ until we have done one page's worth (from byte #247 to \ #1)

Code variation 11 of 13Related to the screen mode

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

6502SP, Master

INC SC+1 \ We have now blanked a whole text row, so increment \ SC+1 so that SC(1 0) points to the next row DEX \ Decrement the row counter in X BNE CLYL \ Loop back to blank another row, until we have done the \ number of rows in X

Code variation 12 of 13A variation in the comments only

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

6502SP

\INX \ These instructions are commented out in the original \STX SC \ source

Code variation 13 of 13Specific to an individual platform

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

Tap on a version to expand it, and tap it again to show to all variations.

Master

6502SP

LDA #%00001001 \ Clear bits 1 and 2 of the Access Control Register at STA VIA+&34 \ SHEILA &34 to switch main memory back into &3000-&7FFF LDA #0 \ Set A = 0 as this is a return value for this routine RTS \ Return from the subroutine
JMP PUTBACK \ Jump to PUTBACK to restore the USOSWRCH handler and \ return from the subroutine using a tail call
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