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Elite on the BBC Micro

Loader: LOGOS [Disc version, Loader 2]

Name: LOGOS [Show more] Type: Subroutine Category: Loader Summary: Print a large Acornsoft logo as part of the loading screen
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * LOADSCR calls LOGOS

Arguments: T The logo colour as a teletext control code for graphics colour ZP(1 0) The address of the Acornsoft logo character table at LOGO
.LOGOS LDY #28 \ Set Y = 28 as an index to the first row of logo \ characters in the table at LOGO, after the 28 bytes of \ lookup data in the first part of the table .aloop LDX #38 \ Each row of the Acornsoft logo consists of 38 teletext \ graphics characters, so set a counter in X to count \ through the characters BIT S \ If bit 7 of S is set (this is an Electron), jump to BMI eskip1 \ eskip1 to skip the teletext colour codes (as the \ Electron loading screen is monochrome) LDA T \ Print the character in T, which starts with teletext JSR OSWRCH \ control code 145 (Red graphics) and increments through \ the colours, so this sets the correct colour for the \ current Acornsoft logo LDA #154 \ Print teletext control code 154 (Separated graphics) JSR OSWRCH CLC \ Skip the next two instructions BCC P%+7 .eskip1 LDA #' ' \ Print a space (on the Electron only) JSR OSWRCH .cloop LDA (ZP),Y \ Fetch the Y-th character from ZP into A, so A contains \ the next byte from LOGO, which is the user-defined \ character we want to print (in the case of the \ Electron), or the index into the first section of the \ LOGO table for the teletext graphics character we want \ to print (in the case of the BBC Micro) BIT S \ If bit 7 of S is set (this is an Electron), jump to BMI eskip2 \ eskip2 STY P \ Store Y so we can retrieve it below TAY \ This is a BBC Micro, so the number in A is the index LDA (ZP),Y \ into the first section of the LOGO table for the \ teletext graphics character we want to print, so we \ now fetch that character LDY P \ Retrieve the value of Y we stored above BNE P%+4 \ Skip the next instruction (this BNE is effectively a \ JMP as Y is never zero) .eskip2 ORA #&E0 \ Add &E0 to the character number (on the Electron only) JSR OSWRCH \ Print the character in A INY \ Increment Y to point to the next byte in the table CPY #255 \ If Y = 255 then we are done printing all 5 rows of the BEQ adone \ logo, so jump to adone to finish off DEX \ Otherwise decrement the character counter in X BNE cloop \ Loop back to print the next character until we have \ done all 38 in this row BIT S \ If bit 7 of S is clear (this is a BBC Micro), skip the BPL P%+7 \ next two instructions LDA #' ' \ Print a space (on the Electron only) JSR OSWRCH CLC \ Jump back to aloop to print the next row in the logo BCC aloop .adone INC T \ Increment the colour in T, which started with teletext \ control code 145 (Red graphics) and increments through \ 146 (green), 147 (yellow) and 148 (blue) with each new \ call to the LOGOS routine RTS \ Return from the subroutine