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