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Elite on the BBC Micro

Text: CHPR [Elite-A, I/O processor]

Name: CHPR [Show more] Type: Subroutine Category: Text Summary: Implement the write_xyc command (write a character to the screen)
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * tube_table calls CHPR

This routine is run when the parasite sends a write_xyc command. It writes a text character to the screen at specified position. If the character is null (i.e. A = 0) then it just moves the text cursor and doesn't print anything.
.CHPR JSR tube_get \ Get the parameters from the parasite for the command: STA XC \ JSR tube_get \ write_xyc(x, y, char) STA YC \ JSR tube_get \ and store them as follows: \ \ * XC = text column (x-coordinate) \ \ * YC = text row (y-coordinate) \ \ * A = the character to print CMP #' ' \ If we are not printing a space character, jump to BNE tube_wrch \ tube_wrch to print the character, returning from the \ subroutine using a tail call LDA #9 \ We are printing a space, so set A to 9 and fall \ through into tube_wrch to print the character