203 lines
7.7 KiB
NASM
203 lines
7.7 KiB
NASM
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;==================================================================================
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; Contents of this file are copyright Grant Searle
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;
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; You have permission to use this for NON COMMERCIAL USE ONLY
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; If you wish to use it elsewhere, please include an acknowledgement to myself.
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;
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; http://searle.hostei.com/grant/index.html
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;
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; eMail: home.micros01@btinternet.com
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;
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; If the above don't work, please perform an Internet search to see if I have
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; updated the web page hosting service.
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;
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;==================================================================================
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; Minimum 6850 ACIA interrupt driven serial I/O to run modified NASCOM Basic 4.7
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; Full input buffering with incoming data hardware handshaking
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; Handshake shows full before the buffer is totally filled to allow run-on from the sender
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SER_BUFSIZE .EQU 3FH
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SER_FULLSIZE .EQU 30H
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SER_EMPTYSIZE .EQU 5
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RTS_HIGH .EQU 0D6H
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RTS_LOW .EQU 096H
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serBuf .EQU $2000
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serInPtr .EQU serBuf+SER_BUFSIZE
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serRdPtr .EQU serInPtr+2
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serBufUsed .EQU serRdPtr+2
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basicStarted .EQU serBufUsed+1
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TEMPSTACK .EQU $20ED ; Top of BASIC line input buffer so is "free ram" when BASIC resets
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CR .EQU 0DH
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LF .EQU 0AH
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CS .EQU 0CH ; Clear screen
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.ORG $0000
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;------------------------------------------------------------------------------
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; Reset
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RST00 DI ;Disable interrupts
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JP INIT ;Initialize Hardware and go
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;------------------------------------------------------------------------------
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; TX a character over RS232
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.ORG 0008H
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RST08 JP TXA
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;------------------------------------------------------------------------------
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; RX a character over RS232 Channel A [Console], hold here until char ready.
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.ORG 0010H
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RST10 JP RXA
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;------------------------------------------------------------------------------
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; Check serial status
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.ORG 0018H
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RST18 JP CKINCHAR
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;------------------------------------------------------------------------------
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; RST 38 - INTERRUPT VECTOR [ for IM 1 ]
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.ORG 0038H
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RST38 JR serialInt
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;------------------------------------------------------------------------------
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serialInt: PUSH AF
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PUSH HL
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IN A,($80)
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AND $01 ; Check if interupt due to read buffer full
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JR Z,rts0 ; if not, ignore
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IN A,($81)
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PUSH AF
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LD A,(serBufUsed)
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CP SER_BUFSIZE ; If full then ignore
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JR NZ,notFull
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POP AF
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JR rts0
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notFull: LD HL,(serInPtr)
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INC HL
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LD A,L ; Only need to check low byte becasuse buffer<256 bytes
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CP (serBuf+SER_BUFSIZE) & $FF
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JR NZ, notWrap
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LD HL,serBuf
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notWrap: LD (serInPtr),HL
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POP AF
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LD (HL),A
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LD A,(serBufUsed)
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INC A
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LD (serBufUsed),A
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CP SER_FULLSIZE
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JR C,rts0
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LD A,RTS_HIGH
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OUT ($80),A
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rts0: POP HL
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POP AF
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EI
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RETI
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;------------------------------------------------------------------------------
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RXA:
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waitForChar: LD A,(serBufUsed)
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CP $00
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JR Z, waitForChar
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PUSH HL
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LD HL,(serRdPtr)
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INC HL
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LD A,L ; Only need to check low byte becasuse buffer<256 bytes
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CP (serBuf+SER_BUFSIZE) & $FF
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JR NZ, notRdWrap
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LD HL,serBuf
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notRdWrap: DI
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LD (serRdPtr),HL
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LD A,(serBufUsed)
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DEC A
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LD (serBufUsed),A
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CP SER_EMPTYSIZE
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JR NC,rts1
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LD A,RTS_LOW
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OUT ($80),A
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rts1:
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LD A,(HL)
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EI
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POP HL
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RET ; Char ready in A
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;------------------------------------------------------------------------------
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TXA: PUSH AF ; Store character
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conout1: IN A,($80) ; Status byte
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BIT 1,A ; Set Zero flag if still transmitting character
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JR Z,conout1 ; Loop until flag signals ready
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POP AF ; Retrieve character
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OUT ($81),A ; Output the character
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RET
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;------------------------------------------------------------------------------
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CKINCHAR LD A,(serBufUsed)
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CP $0
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RET
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PRINT: LD A,(HL) ; Get character
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OR A ; Is it $00 ?
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RET Z ; Then RETurn on terminator
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RST 08H ; Print it
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INC HL ; Next Character
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JR PRINT ; Continue until $00
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RET
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;------------------------------------------------------------------------------
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INIT:
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LD HL,TEMPSTACK ; Temp stack
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LD SP,HL ; Set up a temporary stack
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LD HL,serBuf
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LD (serInPtr),HL
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LD (serRdPtr),HL
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XOR A ;0 to accumulator
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LD (serBufUsed),A
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LD A,RTS_LOW
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OUT ($80),A ; Initialise ACIA
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IM 1
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EI
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LD HL,SIGNON1 ; Sign-on message
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CALL PRINT ; Output string
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LD A,(basicStarted); Check the BASIC STARTED flag
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CP 'Y' ; to see if this is power-up
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JR NZ,COLDSTART ; If not BASIC started then always do cold start
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LD HL,SIGNON2 ; Cold/warm message
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CALL PRINT ; Output string
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CORW:
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CALL RXA
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AND %11011111 ; lower to uppercase
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CP 'C'
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JR NZ, CHECKWARM
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RST 08H
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LD A,$0D
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RST 08H
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LD A,$0A
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RST 08H
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COLDSTART: LD A,'Y' ; Set the BASIC STARTED flag
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LD (basicStarted),A
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JP $0150 ; Start BASIC COLD
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CHECKWARM:
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CP 'W'
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JR NZ, CORW
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RST 08H
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LD A,$0D
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RST 08H
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LD A,$0A
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RST 08H
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JP $0153 ; Start BASIC WARM
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SIGNON1: .BYTE CS
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.BYTE "Z80 SBC By Grant Searle",CR,LF,0
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SIGNON2: .BYTE CR,LF
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.BYTE "Cold or warm start (C or W)? ",0
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.END
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