77 lines
2.5 KiB
NASM
77 lines
2.5 KiB
NASM
; 6502 BIOS
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; Based on original code by Daryl Rictor
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; Adapted to Real Retro UART board for RC2014
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; Renamed to rruart.asm
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;
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; ----------------- assembly instructions ----------------------------
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;
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; this is a subroutine library only
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; it must be included in an executable source file
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;
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;
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;*** I/O Locations *******************************
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; Define the i/o address of the UART chip
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;*** Real Retro UART ************************
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uart_base = $c040
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uart_xmit = $c040
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uart_recv = $c040
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uart_status = $c041
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;
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;***********************************************************************
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; UART I/O Support Routines
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;---------------------------------------------------------------------
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;
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uart_init
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; Nothing to init
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ldx #4
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lda #$0a
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ui_loop
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jsr uart_output
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dex
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bne ui_loop
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lda #$0d
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jsr uart_output
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rts ; done
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;---------------------------------------------------------------------
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; Input char from UART (blocking)
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; Exit: character in A
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uart_input
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lda uart_status ; Serial port status
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and #$01 ; is recvr full
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beq uart_input ; no char to get
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lda uart_recv ; get chr
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rts ;
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;---------------------------------------------------------------------
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; Non-waiting get character routine
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; Scan for input (no wait), C=1 char, C=0 no character
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uart_scan
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clc
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lda uart_status ; Serial port status
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and #$01 ; mask rcvr full bit
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beq uart_scan2
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lda uart_recv ; get chr
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sec
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uart_scan2 rts
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;---------------------------------------------------------------------
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; output to OutPut Port
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; Entry: character in A
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; Exit: character in A
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uart_output
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pha ; save registers
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uart_out1
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lda uart_status ; serial port status
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and #$02 ; is tx buffer empty
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beq uart_out1 ; no
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pla ; get chr
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sta uart_xmit ; put character to Port
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rts ; done
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;
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;end of file
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