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Version analysis of MT26

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

Code variations between these versions are shown below.

Name: MT26 Type: Subroutine Category: Text Summary: Fetch a line of text from the keyboard Deep dive: Extended text tokens

Code variation 1 of 7A variation in the comments only

This variation is blank in the Master version.

If ESCAPE is pressed or a blank name is entered, then an empty string is returned.
Returns: Y The size of the entered text, or 0 if none was entered

Code variation 2 of 7A variation in the comments only

This variation is blank in the Master version.

or if ESCAPE was pressed
INWK+5 The entered text, terminated by a carriage return C flag Set if ESCAPE was pressed
.MT26

Code variation 3 of 7Related to the Master version

When entering text in the Master version, the text that is typed is shown in magenta, while it is shown in white in the other versions.

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

LDA COL \ Store the current colour on the stack PHA LDA #RED \ Switch to colour 2, which is magenta in the trade view STA COL

Code variation 4 of 7Related to Elite's use of the Tube

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

LDA #%10000001 \ Clear 6522 System VIA interrupt enable register IER STA VIA+&4E \ (SHEILA &4E) bit 1 (i.e. enable the CA2 interrupt, \ which comes from the keyboard)
LDY #8 \ Wait for 8/50 of a second (0.16 seconds) JSR DELAY JSR FLKB \ Call FLKB to flush the keyboard buffer
LDA #VIAE \ Send a #VIAE %10000001 command to the I/O processor to JSR OSWRCH \ clear 6522 System VIA interrupt enable register IER LDA #%10000001 \ (SHEILA &4E) bit 1 (i.e. enable the CA2 interrupt, JSR OSWRCH \ which comes from the keyboard) LDY #8 \ Wait for 8/50 of a second (0.16 seconds) JSR DELAY

Code variation 5 of 7Related to the Master version

The Master version contains its own custom routine for the extended token that asks for a line of text, while the other enhanced versions use the standard OSWORD command. The Master Compact version of that custom routine supports more characters, as it supports ADFS rather than DFS.

See below for more variations related to this code.

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

JSR FLKB \ Call FLKB to flush the keyboard buffer LDX #LO(RLINE) \ Set (Y X) to point to the RLINE parameter block LDY #HI(RLINE) LDA #0 \ Call OSWORD with A = 0 to read a line from the current JSR OSWORD \ input stream (i.e. the keyboard) BCC P%+4 \ The C flag will be set if we pressed ESCAPE when \ entering the name, otherwise it will be clear, so \ skip the next instruction if ESCAPE is not pressed LDY #0 \ ESCAPE was pressed, so set Y = 0 (as the OSWORD call \ returns the length of the entered string in Y)
LDY #0 \ Set Y = 0 to hold the length of the text entered .OSW0L JSR TT217 \ Scan the keyboard until a key is pressed, and return \ the key's ASCII code in A (and X) CMP #13 \ If RETURN was pressed, jump to OSW03 BEQ OSW03 CMP #27 \ If ESCAPE was pressed, jump to OSW04 BEQ OSW04 CMP #127 \ If DELETE was pressed, jump to OSW05 BEQ OSW05 IF _COMPACT PHX \ Store X on the stack so we can retrieve it after the \ call to SHIFT PHA \ Store the number of the key being pressed on the stack JSR SHIFT \ If SHIFT is not being pressed, jump to noshift to skip BPL noshift \ the following PLA \ SHIFT is being pressed, so fetch the number of the key \ being pressed from the stack CMP #'@' \ If A >= ASCII "@", then we are pressing a letter key, BCS P%+4 \ so skip the following instruction EOR #%00010000 \ We are pressing SHIFT and a number key, so flip bit 4 \ of the key number, which flips the letter between the \ ASCII code of the number being pressed and the ASCII \ code of the number being pressed when SHIFT is being \ held down (so SHIFT-1 will enter !, SHIFT-2 will enter \ ", and so on) PHA \ Push the updated key number onto the stack .noshift PLA \ Retrieve the values of X and A we stored on the stack PLX \ above ENDIF CPY RLINE+2 \ If Y >= RLINE+2 (the maximum line length from the BCS OSW01 \ OSWORD configuration block at RLINE), then jump to \ OSW01 to give an error beep as we have reached the \ character limit CMP RLINE+3 \ If the key pressed is less than the character in BCC OSW01 \ RLINE+3 (the lowest allowed character from the OSWORD \ configuration block at RLINE), then jump to OSW01 \ to give an error beep as the key pressed is out of \ range CMP RLINE+4 \ If the key pressed is greater than or equal to the BCS OSW01 \ character in RLINE+4 (the highest allowed character \ from the OSWORD configuration block at RLINE), then \ jump to OSW01 to give an error beep as the key \ pressed is out of range STA INWK+5,Y \ Store the key's ASCII code in the Y-th byte of INWK+5 INY \ Increment Y to point to the next free byte in INWK+5 EQUB &2C \ Skip the next instruction by turning it into \ &2C &A9 &07, or BIT &07A9, which does nothing apart \ from affect the flags .OSW01 LDA #7 \ Set A to the beep character, so the next instruction \ makes a system beep .OSW06 JSR CHPR \ Print the character in A (and clear the C flag) BCC OSW0L \ Loop back to OSW0L to fetch another key press (this \ BCC is effectively a JMP as CHPR clears the C flag) .OSW03 STA INWK+5,Y \ Store the return character in the Y-th byte of INWK+5 LDA #12 \ Print a newline JSR CHPR EQUB &24 \ Skip the next instruction by turning it into &24 &38, \ or BIT &0038, which does nothing apart from affect the \ flags .OSW04 SEC \ Set the C flag as ESCAPE was pressed PLA \ Restore the original colour from the stack and set it STA COL \ as the current colour RTS \ Return from the subroutine .OSW05 TYA \ If the length of the line so far in Y is 0, then we BEQ OSW01 \ just pressed DELETE on an empty line, so jump to \ OSW01 give an error beep DEY \ Otherwise we want to delete a character, so decrement \ the length of the line so far in Y LDA #127 \ Set A = 127 and jump back to OSW06 to print the BNE OSW06 \ character in A (i.e. the DELETE character) and listen \ for the next key press

Code variation 6 of 7Related to Elite's use of the Tube

This variation is blank in the Master version.

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

LDA #%00000001 \ Set 6522 System VIA interrupt enable register IER STA VIA+&4E \ (SHEILA &4E) bit 1 (i.e. disable the CA2 interrupt, \ which comes from the keyboard)
LDA #VIAE \ Send a #VIAE %00000001 command to the I/O processor to JSR OSWRCH \ set 6522 System VIA interrupt enable register IER LDA #%00000001 \ (SHEILA &4E) bit 1 (i.e. disable the CA2 interrupt, JSR OSWRCH \ which comes from the keyboard)

Code variation 7 of 7Related to the Master version

See variation 5 above for details.

This variation is blank in the Master version.

JMP FEED \ Jump to FEED to print a newline, returning from the \ subroutine using a tail call