; I2OS-1.ASM - Osborne OS-1 overlay file for IMP - 10/27/85 ; ; 6850 ACIA ; ; NOTE ..... This overlay will NOT, repeat, NOT work with the ; Osborne COMM-PAC modem or the CTS DATACOMM modem. ; These two modems are 300 bps only and do not have ; the faster baud rates necessary to take advantage ; of the IMP program. ; ; The new 1K CRC protocol is not supported at 300 ; bps in IMP or KMD. In addition, YAM batch transfers ; with IMP and KMD are supported only with 1K CRC ; protocol at 1200 and 2400 bps. ; ; No real advantage is gained with using IMP at 300 ; bps. Osborne COMM-PAC and CTS DATACOMM users ; should continue to use MDM740. ; ;----------------------------------------------------------------------- ; ; Edit this file for your preferences then follow the "TO USE:" example ; shown below. ; ; Many terminals will clear the screen with a CTL-Z. If yours does, put ; a 1AH at CLEAR: (010AH). Many terminals use two characters, the first ; normally an ESC. For example, ESC *. In this case put '*' at CLEAR: ; (The ESC will automatically be typed with no CTL-character present.) ; If you don't know what your terminal uses, put a 0 at CLEAR: and IMP2 ; will scroll up 24 blank lines to clear the CRT for things like MENU, ; looking at the function key table, typing CTL-Z in command mode, etc. ; ; Use the "SET" command to change the baudrate when desired. The value ; at MSPEED controls the baudrate when the program is first called up. ; ; TO USE: First edit this file filling in answers for your own ; equipment. Then assemble with ASM.COM or equivalent ; assembler. Then use MLOAD to merge into the main file: ; ; MLOAD IMP.COM=IMP2xx.COM,I2OS-x.HEX ; ; = = = = = = = = = = = = = = = = = = ; ; 10/27/85 Modified for Osborne 1 computer - Roy Robinson ; two hardware equates added FOG #4 RCP/M ; (415) 591-6259 ; 06/27/85 Written for use with IMP2 - Irv Hoff ; ; = = = = = = = = = = = = = = = = = ; ; ; DOCUMENTATION FOR THIS IMP OVERLAY: ; ;------------------- ; ; If you intend to use this overlay with none of the hardware modifica- ; tions to the main logic board described in this overlay, set the ; DTRMOD equate to NO. You will have the following baud rate selections: ; 300 and 1200 bps. An unmodified Osborne 1 will not work if the DTRMOD ; equate is set to YES. ; ; The NUEVO equate concerns the use of a "piggy-back" 80 column video ; board made by NUEVO ELECTRONICS with an optional baud rate generator. ; NUEVO ELECTRONICS may be contacted at: (713) 341-6001. ; ;------------------- ; The NUEVO equate: ; ; If you have the NUEVO 80 column video board with the baud rate option ; installed, set the NUEVO equate to YES. You will then have the fol- ; lowing baud rate selections: 300, 1200, 2400, 4800, 9600, and 19,200 ; bps. Setting either the HS1200 or HS2400 equate to YES, along with ; the matching MSPEED value will configure IMP2 to 1200 or 2400 bps re- ; spectively when the program is executed. ; ; If your NUEVO 80 column board does NOT have the optional baud rate ; generator, set the NEUVO equate to NO. Since the NUEVO baud rate ; generator is not installed, you will have the following baud rate ; selections: 300 and 1200 bps. ; ; Contact NUEVO ELECTRONICS if you wish to install the baud rate option ; on your NUEVO 80 column board. ; ;-------------------- ;The DTRMOD equate: ; ; If you decide to install the DTR modification to your Osborne 1 main ; logic board, set the DTRMOD equate to YES. This DTR modification can ; be installed in an Osborne 1 with or without the Osborne or NUEVO 80 ; column video boards. The DTR modification gives the Osborne 1 the ; ability to force the modem to hang up the phone by dropping the 6850 ; ACIA RTS line which is connected to the modem DTR input. The modifi- ; cation offers the Osborne 1 hardware control of the modem, rather than ; depending on the software generated "ATH" modem command. ; ; The DTR modification is required if your modem does not follow the ; Hayes/Racal-Vadic/USRobotics/Prometheus modem software commands. ; ; If you do use the DTR modification, you will need to configure a spe- ; cial RS-232 cable from your Osborne 1 serial port to your external ; modem. Your modem must support the DTR input signal line and you must ; set the modem DTR switch or program the modem internal memory to moni- ; tor its DTR signal input. ; ; New RS-232 modem cable to be used with OCC-1 and external modem when ; using DTR control: ; ; ; OCC-1 MODEM ; ; 2 RXD 3 RXD ; 3 TXD 2 TXD ; 5 RTS (new function) 20 DTR ; 7 GND 7 GND ; ; DTR SUPPORT MODIFICATION ; ; OSBORNE 1 MAIN LOGIC BOARD TRACE CUTS: ; The Osborne 1 main logic board is organized into zones which are iden- ; tified on the COMPONENT side of the main logic board with LETTERS found ; along the left side of the board and NUMBERS found along the rear of ; the board (i.e., the 6850 ACIA device is located in zones C4, C5, and ; C6 and the MC1458 device is located in zone E3). If you are unsure ; how to count pin numbers on IC devices, find a friend who does, attend ; a user group meeting, or take your computer to a computer store/service ; center for further aid. ; ; -------------------------- ; Solder Side: ; ; Cut the trace running from pin 5 to pin 6 on the inner row of pads ; used to mount the RS-232 female serial connector at the front of the ; main logic board. Pin 1 is the pad with a wide ground trace. ; ; Component side: ; ; Cut the trace from pin 5 of the 6850 ACIA device in zone C4 to resistor ; R20 (10K ohm) located in zone D5. ; ; PART ADDITIONS: ; -------------- ; Solder side: ; ; Add a jumper wire from pin 1 of the MC1458 device in zone E3 to pin 5 ; on the inner row of the RS-232 serial port pads. ; Pin 1 is the pad with the wide ground trace. ; ; Add a jumper wire from pin 3 of the MC1458 device in zone E3 to pin 5 ; of the same MC1458 device in zone E3. ; ; Using the component side or solder side (whichever side you feel more ; comfortable for mounting the two - 1/4 watt resistors): ; ; Mount a 10K ohm resistor from Vcc which is +5 volts (pin 14 of the ; 74LS02 device in zone D2 is a good solder point) to pin 2 of the MC1458 ; device in zone E3. ; ; Mount a 220 ohm resistor from pin 5 of the 6850 ACIA device in zone ; C4 to pin 2 of the MC1458 device in zone E3. Pin 2 of the MC1458 ; device in zone E3 should now have two resistors attached to it. ; ; = = = = = = = = = = = = = = = = = = ; ;* TAMPERING WITH YOUR MAIN LOGIC BOARD MAY VOID ANY WARRANTY ; OR SERVICE AGREEMENTS ON YOUR COMPUTER. ;* UNPLUG YOUR COMPUTER FROM THE AC OUTLET BEFORE ; DISASSEMBLING THE COMPUTER. USE COMMON SENSE. ;* ALTHOUGH THE MODIFICATION HAS BEEN TESTED ON SEVERAL MAIN ; LOGIC BOARDS HAVING DIFFERENT REVISION LEVELS, THE ; MODIFICATION IS DONE AT YOUR OWN RISK. ; ;* INSTALLATING THIS DTR MODIFICATION WILL NO LONGER ALLOW YOU ; TO USE THE 9 PIN MODEM PORT WITH THE COMM-PAC OR DATACOMM ; MODEMS. ; ; = = = = = = = = = = = = = = = = = = ; ; YES EQU 0FFH NO EQU 0 ; ; ; EQUATES FOR MODIFICATIONS TO STANDARD OZZIE MAIN LOGIC BOARD ; DTRMOD EQU NO ; YES, if hardware mods have been installed on ; Osborne 1 main logic board to support DTR ; control of external modem. ; Do not set to YES if you have not installed ; DTR modifications. ; (see discussion above) ; NUEVO EQU NO ; YES, if Nuevo 80 column upgrade WITH baud rate ; option has been installed ; (see discussion above) ; ; Values shown are for the 6850 ACIA serial I/O device ; PORT EQU 2A00H ; OCC-1 base address ; (memory mapped for data and status) MDCTL1 EQU PORT ; Modem control address (memory mapped i/o) MDDATP EQU PORT+1 ; Modem data address (memory mapped i/o) MDRCV EQU 01H ; Modem receive data register full (RDRF) MDSND EQU 02H ; Modem transmit data register empty (TDRE) MDTXE EQU 02H ; Modem transmit buffer empty (set to MDSND) RMDRCV EQU 0FEH ; Used with SSTAT routines RMDSND EQU 0FDH ; Used with SSTAT routines ; ; ;----------------------------------------------------------------------- ; ESC EQU '['-40H ; ^[ = Escape BELL EQU 'G'-40H ; ^G = Bell character LF EQU 'J'-40H ; ^J = Linefeed NEXTRY EQU 'K'-40H ; ^K = Try next phone number, abort this try CR EQU 'M'-40H ; ^M = Carriage return CLEARSC EQU 'Z'-40H ; ^Z = Clears screen, command mode only EOFCHAR EQU 'Z'-40H ; ^Z = End of file ; ; ;----------------------------------------------------------------------- ; ; ORG 0100H ; ; DS 3 ; Skip the data area below ; ; ; These routines and equates are at the beginning of the program so ; they can be patched by a monitor or overlay file without re-assembling ; the program. ; MSPEED: DB 5 ; 0=110 1=300 2=450 3=600 4=710 5=1200 103H ; 6=2400 7=4800 8=9600 9=19200 default HS2400: DB NO ; Yes=2400 bps highest speed 104H HS1200: DB YES ; Yes=1200 bps highest speed 105H RACAL: DB NO ; Yes=Racal-Vadic 1200V or 2400V or 2400PA 106H PROMODM: DB NO ; Yes=Prometheus ProModem 1200 bps 107H RESVD1: DB NO ; Reserved for special modems 108H RESVD2: DB NO ; Reserved for special modems 109H ; ; CLEAR: DB 1AH ; Clear screen character (ESC not needed) 10AH CLOCK: DB 40 ; Clock speed in MHz x10, 25.5 MHz max. 10BH ; 20=2 MHh, 37=3.68 MHz, 40=4 MHz, etc. BYTDLY: DB 2 ; 0=0 delay 1=10ms 5=50 ms - 9=90 ms 10CH ; default time to send character in ter- ; minal mode file transfer for slow BBS CRDLY: DB 2 ; 0=0 delay 1=100 ms 5=500 ms - 9=900 ms 10DH ; default time for extra wait after CRLF ; in terminal mode file transfer NOFCOL: DB 5 ; Number of directory columns shown 10EH TCHPUL: DB 'T' ; T=tone, P=Pulse (Hayes 2400 modems) 10FH ;..... ; ; ADDLFD: DB NO ; Yes=add LF after CR to send file in terminal 110H ; mode (normally added by remote echo) CONVRUB: DB YES ; Yes=convert rub to backspace 111H CRCDFLT: DB YES ; Yes=default to CRC checking 112H IGNRCTL: DB NO ; Yes=CTL-chars above ^M not displayed 113H ;..... ; ; EXTCHR: DB '['-40H ; ESC = preceeds local control character 114H EXITCHR: DB 'E' ; Exit character 115H FILESND: DB 'F' ; Send file when in terminal mode 116H NOCONCT: DB 'N' ; Disconnect from phone line 117H LOGCHR: DB 'L' ; Send logon 118H LSTCHR: DB 'P' ; Toggle printer 119H UNSAVCH: DB 'R' ; Close input text buffer 11AH SAVECHR: DB 'Y' ; Open input text buffer 11BH CLEARS: DB 'Z' ; Clears screen, terminal mode 11CH SPARE1: DB 0 ; For future development 11DH NODTR: DB NO ; Yes if no DTR and using +++ to disconnect 11EH ;..... ; ; ; Handles in/out ports for data and status ; I$MDCTL1: CALL OSTAT ; 11FH RET ; 122H DB 0,0,0,0,0,0 ; Spares if needed 123H ; I$MDTXE: CALL OSTAT ; 129H RET ; 12CH DB 0,0,0,0,0,0 ; Spares if needed 12DH ; I$MDDATP: CALL OSIN ; 133H RET ; 136H DB 0,0,0,0,0,0 ; Spares if needed 137H ; O$MDDATP: CALL OSOUT ; 13DH RET ; 140H DB 0,0,0,0,0,0 ; Spares if needed 141H ;..... ; ; A$MDRCV: ANI MDRCV ; 147H RET ; 149H ; C$MDRCV: CPI MDRCV ; 14AH RET ; 14CH ; A$MDSND: ANI MDSND ; 14DH RET ; 14FH ; C$MDSND: CPI MDSND ; 150H RET ; 152H ; A$MDTXE: ANI MDTXE ; 153H RET ; 155H ; C$MDTXE: CPI MDTXE ; 156H RET ; 158H ;..... ; ; ; Special exit vector, used by some computers to reset interrupt vectors ; J$EXITVEC: JMP RSTINT ; 159H ;..... ; ; ; Jump vectors needed by each overlay ; J$GOODBYE:JMP GOODBYE ; Disconnects modem by dropping DTR 15CH J$INITMOD:JMP INITMOD ; Initializes modem, autosets baudrate 15FH J$STUPR: JMP STUPR ; SET routine to change baudrate 162H J$SYSVR: JMP SYSVR ; Signon message 165H ;..... ; ; ; "AT" command strings, can be replaced in individual overlay if needed ; J$STRNGA: DS 3 ; 1200 bps "AT" string 168H J$STRNG1: DS 3 ; 2400 bps "AT" string 16BH ; ; ; Next fourteen lines should not be changed by user overlay as these go ; to specific locations in the main program, not in the overlay. ; ; J$CMDSPL: DS 3 ; Allows entry of baudrate on CMD line 16EH J$CRLF: DS 3 ; Turns up one new line on display 171H J$DIAL: DS 3 ; Start of dialing routine 174H J$DSCONT: DS 3 ; Terminates modem use 177H J$GOLST: DS 3 ; Printer routine, needed by Apple //e 17AH J$ILPRT: DS 3 ; Prints an inline string, 0 to end 17DH J$INBUF: DS 3 ; Stores a keybd string for comparison 180H J$INLNCP: DS 3 ; Inline "compare strings" routine 183H J$INMDM: DS 3 ; Max .1 sec wait for modem character 186H J$RCVRSP: DS 3 ; For 3801 I/O use (TV-803) 189H J$SNDCHR: DS 3 ; Sends a character to the modem 18CH J$SNDSTR: DS 3 ; Sends a string to the modem, $ to end 18FH J$TIMER: DS 3 ; .1 second timer (amount in 'B' reg.) 192H J$NEW1: DB 0,0,0 ; For future needs 195H J$NEW2: DB 0,0,0 ; For future needs 198H ;..... ; ; ; For 2400 bps auto-stepdown units ; MANUAL: DB 0 ; For manual selection flag 19BH J$300: JMP OK300 ; Sets baudrate to 300 baud 19CH J$1200: JMP OK1200 ; Sets baudrate to 1200 bps 19FH J$2400: JMP OK2400 ; Sets baudrate to 2400 bps 1A2H ;..... ; ; LOGPTR: DW LOGON ; Pointer to display LOGON message 1A5H ; SYSVR: CALL J$ILPRT ; Display the following line 1A7H DB 'Version for Osborne 1 Computer' ; 1AAH ; IF NUEVO DB ' with Neuvo 80 column upgrade and baud rate option' ENDIF ; NUEVO ; DB CR,LF ; IF DTRMOD DB 'DTR supported',CR,LF ENDIF ; DTRMOD ; IF NOT DTRMOD DB 'DTR not supported',CR,LF ENDIF ; NOT DTRMOD ; DB CR,LF,0 RET ;..... ; ; ;----------------------------------------------------------------------- ; ; NOTE: You can change the SYSVER message to be longer or shorter. The ; end of your last routine should terminate by 0400H (601 bytes ; available after start of SYSVER). ; ;----------------------------------------------------------------------- ; ; You can put in a message at this location which can be called up with ; (special character-L). You can put in several lines. End with a 0. ; LOGON: DB 'Greetings from an Osborne 1 user',CR,LF,0 ; ;----------------------------------------------------------------------- ; ; ; This routine sets RTS output low for 300 ms to disconnect the phone. ; RTS output from 6850 is connected to the DTR input of the modem. ; GOODBYE: MVI B,'S'-40H ; X-off to stop host if needed CALL J$SNDCHR MVI B,1 ; Wait a moment to let it react CALL J$TIMER ; IF DTRMOD MVI C,77H ; Send break, RTS active, CALL STBAUD ; Send to status port routine MVI B,3 ; Delay 300 ms to hang up phone CALL J$TIMER MVI C,57H ; Turn off break and disable RTS CALL STBAUD ; Send to status port routine MVI B,1 ; Slight delay CALL J$TIMER LDA BAUDRTE ; Normal I/O RTS active, same baud rate MOV C,A JMP STBAUD ; Send to status port routine ENDIF ; DTRMOD ; RET ;..... ; ; ; You can use this area for any special initialization or setup you may ; wish to include. Each must stop with a RET. You can check the other ; available overlays for ideas how to write your own routines if that ; may be of some help. ; ; INITMOD: LHLD 0005H+1 ; Find start of bdos LXI D,-0100H ; Go to first page ahead of bdos DAD D ; HL now positioned one page below bdos PUSH H ; Save the address LXI D,BDJ ; Point to our routine to put there LXI B,CDLEN+2 ; Set length of code XCHG DB 0EDH,0B0H ; Z80 LDIR instruction ; LHLD 0005H+1 ; Get bdos address back once more POP D ; Get starting address off the stack PUSH D ; Put it back on the stack INX D ; Point to address position XCHG ; Put into HL register pair MOV M,E ; Store 'LSP' address INX H ; Get 'LSP' location MOV M,D ; Store 'MSP' address POP H ; Get the address back once more SHLD 0005H+1 ; New address to protect from overwrite ; LXI D,OSIN-BDJ ; Get length of routine to move DAD D ; Commute address of the OSIN routine SHLD I$MDDATP+1 ; Patch call for "GET CHARACTER" routine LXI D,OSOUT-OSIN DAD D SHLD O$MDDATP+1 ; Patch call for "SEND CHARACTER" routine LXI D,OSTAT-OSOUT DAD D SHLD I$MDCTL1+1 ; Patch call for "ACIA STATUS" routine SHLD I$MDTXE+1 ; Patch call for "TRANSMIT BUFFER EMPTY" ; ; ; Set requested baud rate then finished with initialization ; LDA MSPEED ; Get the selected value CPI 1 ; 300 bps JZ OK300 CPI 5 ; 1200 bps JZ OK1200 ; IF NUEVO CPI 6 ; 2400 bps JZ OK2400 ENDIF ; NUEVO ; JMP STUPR1 ; Else ask what is wanted ;...... ; ; ;----------------------------------------------------------------------- ; RSTINT: JMP 0000H ; Osborne 1 likes this jump upon exit ;..... ; ; ;----------------------------------------------------------------------- ; ; STUPR: CALL J$CMDSPL ; Gives us CMDBUF+6 JNC STUPR2 ; STUPR1: CALL J$ILPRT ; IF NOT NUEVO DB 'Input Baud Rate (300, 1200): ',0 ENDIF ; NOT NUEVO ; IF NUEVO DB 'Input Baud Rate (300, 1200, 2400, 4800, ' DB '9600, 19200): ',0 ENDIF ; NUEVO ; LXI D,BAUDBUF ; Point to new input buffer CALL J$INBUF CALL J$CRLF LXI D,BAUDBUF+2 ; STUPR2: CALL J$INLNCP ; Compare BAUDBUF+2 with chars. below DB '300',0 JNC OK300 ; Go if got match CALL J$INLNCP DB '1200',0 JNC OK1200 ; IF NUEVO CALL J$INLNCP DB '2400',0 JNC OK2400 CALL J$INLNCP DB '4800',0 JNC OK4800 CALL J$INLNCP DB '9600',0 JNC OK9600 CALL J$INLNCP DB '19200',0 JNC OK19200 ENDIF ; NUEVO ; CALL J$ILPRT ; All matches failed, tell operator DB '++ Incorrect entry ++',CR,LF,BELL,CR,LF,0 JMP STUPR1 ; Try again ;... ; ; IF NOT NUEVO OK300: MVI A,1 ; MSPEED 300 baud value ENDIF ; NOT NUEVO ; IF NOT NUEVO AND DTRMOD MVI C,16H ; X64 clock, 8 DB 1 SB, RTS active ENDIF ; NOT NUEVO AND DTRMOD ; IF NOT NUEVO AND NOT DTRMOD MVI C,56H ; X64 clock, 8 DB 1 SB, RTS inactive ENDIF ; NOT NUEVO AND NOT DTRMOD ; IF NOT NUEVO JMP LOADBD ; Load ACIA control byte ; OK1200: MVI A,5 ; MSPEED 1200 baud value ENDIF ; NOT NUEVO ; IF NOT NUEVO AND DTRMOD MVI C,15H ; X16 clock, 8 DB 1 SB, RTS active ENDIF ; NOT NUEVO AND DTRMOD ; IF NOT NUEVO AND NOT DTRMOD MVI C,55H ; X16 clock, 8 DB 1 SB, RTS inactive ENDIF ; NOT NUEVO AND NOT DTRMOD ; OK2400: IF NOT NUEVO ; LOADBD: STA MSPEED MOV A,C ; Move ACIA control byte from C to A STA BAUDRTE ; Save ACIA control byte ENDIF ; NOT NUEVO ;... ; ; IF NUEVO OK300: MVI A,1 ; MSPEED 300 baud value MVI C,05H ; Get 300 bps byte JMP LOADBD ; Load baud rate generator control byte ; OK1200: MVI A,5 ; MSPEED 1200 baud value MVI C,07H ; Get 1200 bps byte JMP LOADBD ; Load baud rate generator control byte ; OK2400: XRA A ; Reset to maximum auto-speed for STA MANUAL ; 2400 bps auto-step down modems MVI A,6 ; MSPEED 2400 baud value MVI C,0AH ; Get 2400 bps byte JMP LOADBD ; Load baud rate generator control byte ; OK4800: MVI A,7 ; MSPEED 4800 baud value MVI C,0CH ; Get 4800 bps byte JMP LOADBD ; Load baud rate generator control byte ; OK9600: MVI A,8 ; MSPEED 9600 baud value MVI C,0EH ; Get 9600 bps byte JMP LOADBD ; Load baud rate generator control byte ; OK19200:MVI A,9 ; MSPEED 9600 baud value MVI C,0FH ; Get 9600 bps byte ; LOADBD: STA MSPEED MOV A,C ; Move baud rate byte from c to a OUT 06H ; Send to NUEVO baud rate generator port ENDIF ; NUEVO ; IF NUEVO AND DTRMOD MVI A,15H ; 16X clock, 8 DB 1 SB, RTS active ENDIF ; NUEVO AND DTRMOD ; IF NUEVO AND NOT DTRMOD MVI A,55H ; 16X clock, 8 DB 1 SB, RTS inactive ENDIF ; NUEVO AND NOT DTRMOD ; IF NUEVO STA BAUDRTE ; Save ACIA control byte ENDIF ; NUEVO ;... ; ; STBAUD: PUSH H CALL OSET POP H RET ;..... ; ; OSET: LHLD 1 ; Get bios+3 address MVI L,3CH ; Extended bios routine for baud rate select PCHL ; branch to it ;..... ; ; BAUDBUF:DB 10,0,0,0,0,0 DB 0,0,0,0,0,0 ; BAUDRTE:DB 0 ; Storage location for baud rate byte SSTAT: DB 0 ; RAM location serves as a secondary status register ; for 6850 ACIA status register. ; This RAM register is used since the 6850 ACIA ; clobbers its own internal status register ; (with regard to TDRE and RDRF status bits) when ; data is traveling in both directions via the ; serial port -- important for ascii text uploads. ;..... ; ; ; --- ROUTINES THAT ARE PLACED JUST UNDER BDOS OVERLAYING THE CCP ; BDJ: JMP $-$ ; This gets patched to jump to bdos entry ; OSIN: LDA SSTAT ; Update SSTAT location in RAM ANI RMDRCV ; before inputing data STA SSTAT ; DI ; Disable interrupts OUT 0 ; Switch to alternate bank LDA MDDATP ; Get data input OUT 1 ; Switch to main bank EI ; Re-enable interrupts RET ;..... ; ; OSOUT: DI ; Disable interrupts OUT 0 ; Switch to alternate bank STA MDDATP ; Send data output OUT 1 ; Switch to main bank EI ; Re-enable interrupts ; LDA SSTAT ; Update SSTAT location in RAM ANI RMDSND ; after outputing data STA SSTAT RET ;..... ; ; OSTAT: DI ; Disable interrupts OUT 0 ; Switch to alternate bank LDA MDCTL1 ; Get status byte OUT 1 ; Switch to main bank EI ; Re-enable interrupts ; PUSH B ; Update SSTAT location in RAM MOV B,A ; using current ACIA status register LDA SSTAT ; bits and earlier ACIA status register ORA B ; bits STA SSTAT POP B RET ;..... ; ; CDLEN EQU $-BDJ ; Length of code to relocate ; ; end ;----------------------------------------------------------------------- ; ; NOTE: Must terminate by 0400H ; END