FROM Peek(65) Vol 5 No. 1, Jan. 1984 By: Leroy Erickson Courtesy of OSMOSUS NEWS 3128 Silver Lake Rd. Minneapolis, MN 55418 On any standard OSI Challenger II (C4P or C8P) or Challenger III, the "boot program" is contained in a 2k byte ROM (a 2316). Such a ROM contains 8 "pages", where a page is 256 decimal or 100 hexadecimal bytes. In OSI's ROMs, each page is a totally self-contained program. Out of the 8 available pages, each system uses only 2 or 3 of them addressed at $FFOO, $FEOO and, maybe, $FDOO. The 8 pages in one standard OSI ROM, the Synertek "SYNMON", contain the following routines: Jumper Page PIN Number Name Address Description ------ ---- ---- ------- ----------- 14 0 65V2P $FEOO 65V Monitor for 540 Video and ASCII keyboard 13 1 65VB73 $FFOO ROM BASIC Support for 540 Video & ASCII keyboard 12 2 65K $FDOO Polled keyboard Driver 11 3 65VK $FEOO 65V Monitor for 540 Video and Polled Keyboard 10 4 65VB76 $FFOO ROM BASIC Support for 540 Video & Polled keyboard 9 5 65H $FFOO? CD-74 Hard Disk Boot Code 8 6 65A $FEOO Serial Monitor 7 7 65F3 $FFOO "H/D/M?" Floppy Disk Boot The jumper socket pin numbers are for the 502 & 505 CPU boards. Jumper socket pins 1, 2 & 3 are the select lines for addresses $FDOO, $FEOO & $FFOO, respectively. A standard BASIC in ROM system thus has the following 3 jumpers set - pins 1 to 12, 2 to 11, & 3 to 10. To convert to a floppy disk system, simply connect pin 3 to pin 7 rather than pin 10. To convert to a standard ASCII keyboard, connect pin 2 to pin 14, and pin 3 to pin 13, while leaving pin 1 open. To convert to a disk based serial system, connect pin 2 to pin 8 and pin 3 to pin 7. A serial BASIC in ROM system cannot be supported with this boot ROM. This listing (see Listing 1) is the one for page 7, the floppy disk boot code. To follow what the routine is doing, start with the 6502's three interrupt vectors. On receiving an NMI interrupt (pin 6 of the 6502 pulled to ground), a jump is made to the address contained in locations $FFFA & $FFFB. For an IRQ (pin 4) or BRK instruction, the address in locations $FFFE & $FFFF is used. For a RESET (pin 40, which is connected to the Break key) , addresses $FFFC & $FFFD are used. Notice that the contents of those last 2 locations is $FFAO, indicating that when you press the Break key, all system hardware is initialized (RESET also does that) and a jump to $FFAO is made. From there on, you're on your own. If you have any questions, mail them to me and I'll try to answer them through PEEK. Have fun! LISTING 1 SYNMON ROM Page 7 - Floppy Disk Boot Code *=$FF00 LODADR=$OOFD PAGCNT=$OOFF STRTAD=$2200 DSKPIA=$C000 DSKACI=$C0I0 SCREEN=$D000 HD0C6=SCREEN+$C6 SERPRT=$FC00 HFD00=$FD00 HFE00=$FE00 HFE01=$FE01 HFE0B=$FE0B HFEED=$FEED HFEFC=$FEFC NMIADR=$0130 IRQADR=$0lC0 ; ; *** DISK BOOT SUBROUTINE *** ; HFF00 LDY #$00 ;Select Data Direction Register A STY DSKPIA+l STY DSKPIA ;Assign Port A as all INPUT LDX #$04 ;Select I/O Port A STX DSKPIA+l STY DSKPIA+3 ;Select Data Direction Register B DEY ;Get an FF STY DSKPIA+2 ;Assign Port B as all OUTPUT STX DSKPIA+3 ;Select I/O Port B STY DSKPIA+2 ;Write Port B = all high (FF) LDA #$FB ;Set step direction line to 'IN' BNE HFF27 ;Skip for first pass HFF1E LDA #$02 ;Test for 'Track 0' true BIT DSKPIA ;Read Port-A & mask with TRKO bit BEQ HFF41 ;True - exit this loop LDA #$FF ;Else, set step dir line to 'OUT' STA DSKPIA+2 ;Set step direction to given value JSR HFF99 ;Wait 12 clock cycles AND #$F7 ;Select 'STEP' function ; STA DSKPIA+2 JSR HFF99 ;Wait 12 clock cycles ORA #$08 ;Turn off 'STEP' function STA DSKPIA+2 ; LDX #$18 ;Wait 30,000 clock cyles JSR WAIT ; (30 OR 15 ms) BEQ HFFlE ;Loop back for more steps ; HFF4l LDX #$7F ;Lower the head STX DSKPIA+2 ; JSR WAIT ;Wait about 150,000 cycles ; HFF49 LDA DSKPIA ;Wait for the index hole BMI HFF49 ; ; HFF4E LDA DSKPIA ;Wait until the index hole ;is gone BPL HFF4E ; LDA #$03 ;Reset the ACIA STA DSKACI ; LDA #$58 ;Select - Receive interrupt ;disabled Xmit interrupt ;disabled, 8 data bits, ;even parity, 1 stop bit, ;/1 clock STA DSKACI JSR GETCHR ;Get a byte from the disk STA LODADR+l ;Store as load address hi· ;and save it in X TAX JSR GETCHR ;Get another byte STA LODADR ;Store as load address low JSR GETCHR ;Get a third byte STA PAGCNT .. ;Store it as /I of pages ;to load LDY #$00 ;Clear index register JSR GETCHR ;Get a data byte STA (LODADR),Y ;Save it at current ;location INY ;Bump index BNE HFF6F ;Loop until a page is full INC LODADR+l ;When a page is full, incr ;addr hi, decr the # of ;pages to load DEC PAGCNT ; BNE HFF6F ;Loop until all pages are ;done STX LODADR+l ;Then, restore addr hi ; LDA #$FF ;Lift the head STA DSKPIA+2 ; RTS ;Go home, page zero is ;loaded ; ; *** Timed Wait Routine *** ; ; Wait 1250 * X + 11 machine cycles ; WAIT LDY #$F8 ;2 ; Get a 248, decimal ; HFF87 DEY ;2 ; Inner loop - wait 1240 BNE HFF87 ;2/3 ; machine cycles ; EOR PAGCNT,X ;4 ; waste 4 cycles DEX ;2 ; Wait X * 1250 cycles BNE WAIT ;2/3 ; Loop until done RTS ;6 ; Go home after X*1250+ ;11 cycles ; ; *** Get a byte from the disk *** GETCHR LDA DSKACI ;Wait for ACIA receive flag LSR A ; BCC GETCHR ; LDA DSKACI+l ;It's there, get the byte HFF99 RTS ;And go home ; HFF9A .BYTE 'H/D/M?' ;*** Request Message *** ; ; ; *** RESET Entry Point *** ; RSTADR CLD ;Clear the decimal flag ;* Clear the screen * LDX #$D8 ;Get the high video page# + 1 LDA #$DO ;Get the low video page # STA LODADR+l ;Store it in an indirect register LDY #$00 ;Clear the low byte of the reg STY LODADR LDA #$20 ;Get a blank HFFAD STA (LODADR),Y ;Clear a char INY ;Bump the index BNE HFFAD ;Loop until a page is done INC LODADR+l ;Then inc the page # CPX LODADR+l ;Done with the screen? BNE HFFAD ;No, keep going LDA #$03 ;* Reset the serial port * STA SERPRI ;Reset the ACIA LDA #$Bl ;Select - enable xmit & ;recv interrupts, 8 bit, ;no parity, 2 stop bits, ;/16 clock STA SERPRT ; ; *Print the request Message * ; HFFC2 LDA HFF9A,Y ;Get a char BMI HFFD5 ;Skip when "CLD' reached STA HDOC6,Y ;Start at 4th line, 6th col LDX HFEO1 ;Send to serial only if valid, ; else, skip BNE HFFD2 ; JSR HFEOB ;Call serial out routine HFFD2 INY ;Loop BNE HFFC2 ; HFFD5 LDA HFEO1 ;Test for video or serial systems BNE HFFDF ;Skip if video JSR HFEOO ;Get char from serial ;device then skip, else ;get char from keyboard BCS HFFE2 ; HFFDF JSR HFEED ; HFFE2 CMP #$48 ;Is it an 'H'? BEQ HFFFO ;Yes, do hard disk boot CMP #$44 ;Is it a 'D'? BNE HFFF6 ;No, go to ROM monitor JSR HFFOO ;Yes, load track zero JMP STRTAD ;Then go to $2200 HFFFO JMP HFDOO ;Goto hard disk routine. JSR HFFOO ;** Unreachable code ** HFFF6 JMP (HFEFC) ;Enter ROM monitor NOP ;** Unreachable code ** HFFFA .WORD NMIADR ;NMI Vector HFFFC .WORD RSTADR ;RESET Vector HFFFE .WORD IRQADR ;IRQ Vector .END b