10 GOSUB 90
   20 PRINT"START  "
   30 GOSUB 100
   40 *SAVE SRLLOW.COM 9000 9134
   70 STOP
   80 PRINT A$,"BLOCKS ";L/256
   90 BEGIN=&9000
  100 CODE=&9000
  110 P%=CODE
  120 [OPT 1
  130 .BEGIN LD BC,&0132; load BC the number of bytes to move.
  140 LD DE,&9012; DE the address to move to.
  150 LD HL,&0112; HL the address to move from
  160 LDIR
  170 JP LAD_ADDS; jump and run comldrn.com from its new location &E916.
  180 NOP
  190 NOP
  200 NOP
  210 RET
  220 .RN DEFW &0100; store address to download starting at.
  230 .SAFE DEFW &E8FE; fail safe to stop downloading over runing comldrn.com.
  240 .LAD_ADDS LD HL,(SAFE); 
  250 LD DE,(RN) ; 
  260 CALL CHK_IN ; a routine to clear serial port buffer.
  270 .CHK_START CALL RTS_ON ; handshaking allow PC to download.
  280 CALL RECEIVE ; a routine to to wait for next byte from serial input.
  290 IN A,(&10) ; put serial input into A reg.
  300 LD DE,(RN) ; load DE with address to load at.
  310 CALL RTS_OFF ; set RTS on to hold flow of serial input from PC.
  320 CP 126 ; copare A to "~" ascii 126
  330 CALL Z,LAD_START ; routine to change DN store according to next 4   hex ascii bytes from serial input.
  340 CP 92 ; compare A reg with "/"
  350 LD DE,(RN) ; load DE new start address if changed.
  360 CALL Z,LAD_PROG ; routine that converts and loads hex list into Einstein. 
  370 JR CHK_START ; loop back
  380 RET
  390 .CHK_IN PUSH AF ; routine to clear bytes not wanted for loading.
  400 CALL RTS_ON
  410 .CHKO IN A,(&10);clear buffer
  420 IN A,(&11) ; read 8521A USART register.
  430 BIT 1,A ; see if bit 1 = 0.
  440 JR NZ, CHKO ; if not jump back and clear next byte.
  450 POP AF
  460 RET
  470 .LAD_START PUSH AF ;routine to change address where code will be loaded.
  480 CALL  GT_BYTE ; download next two ascii hex bytes convert to rreal byte
  490 LD D,A ; real byte returned in A reg. then loaded into D reg.
  500 CALL H_PRINT ; routine convert real byte back to ascii and eco to PC terminal.
  510 CALL GT_BYTE ; get next real byte.
  520 LD E,A ; put second byte into E reg.
  530 CALL H_PRINT ; echo second byte to PC.
  540 LD (RN),DE ; store DE for new address to down load to.
  550 POP AF
  560 RET
  570 .LAD_PROG ADD A,00 ; routine to load code into Einstein.
  580 DEC A
  590 DEC A
  600 PUSH HL
  610 PUSH DE
  620 SBC HL,DE ; check to see if loading over runs.
  630 JR Z NO_START ; if so jump to abort
  640 POP DE
  650 POP HL
  660 CALL GT_BYTE; GET TWO ASCI HEX BYTES FOR REAL BYTE
  670   LD (DE),A ; returned byte in A reg. loaded at address given by DE
  680   CALL ECO ; echo loaded byte back to PC terminal.
  690   INC DE ; get next address to load next byte.
  700   JR LAD_PROG ; loop back
  710   RET
  720   .NO_START RET ; fail safe finish.
  730   .GT_BYTE PUSH HL ; the routine to download two hex ascii bytes for real byte.
  740   PUSH DE
  750   CALL RTS_ON ; set handshaking on.
  760   .BACK CALL RECEIVE ; routine to check if new byte has been recieved in 8251A buffer.
  770   IN A,(&10) ; returned new byte in A reg.
  780   CP 71 ; compare A to "G"
  790   JR NC,BACK ; if A greater than 71-ascii G or higher jump back get next byte.
  800   CP 48 ; compare A to "0"
  810   JR C,BACK ; if A smaller than 48 jump back and get next byte.
  820   CALL RTS_OFF ; hardware handshaking to hold down load from PC.
  830   CP 61 ; compare A reg.(next byte) to "="
  840   JR Z,INEND ; if so program down load complete jump to end.  
  850   CP &40 ; compare A to "@" ascii character before  "A"
  860   JR C,WR1 ; jump if A value less than &40-for digets 1 to 9 
  870   AND &DF
  880   SUB 07 ; standardize character code.
  890   .WR1 ADD A,A ; shift A one hex digit left
  900   ADD A,A ; so &30 becomes 00
  910   ADD A,A
  920   ADD A,A
  930   PUSH HL ; store HL
  940   LD L,00
  950   LD H,00
  960   LD H,A ; H=first hex digit * 16
  970   CALL RTS_ON ; hanshacking allows serial input
  980   .BACK2 CALL RECEIVE ; checks for new byte received.
  990   IN A,(&10) ; serial imput returned in A reg.
 1000   CP 71 ; compare A to "G".
 1010   JR NC,BACK2 ; if G or Higher jump back and get next byte.
 1020   CP 48 ; compare A to "0"
 1030   JR C,BACK2 ; if not "0" and ascii characters less than 48.
 1040   CALL RTS_OFF ; handshacking hold serial input.
 1050   CP 61 ; compare A reg. to "=".
 1060   JR Z,INEND ; if so program download complete jump to end.
 1070   CP &40 ;compare A to "@" ascii character before  "A"
 1080   JR C,WR2
 1090   AND &DF
 1100   SUB 07
 1110   .WR2 AND &0F ; consider second hex digit only.
 1120   OR H ; combine with first hex digit-A reg now holds value of two ascii hex bytes.
 1130   POP HL
 1140   POP DE
 1150   POP HL
 1160   RET
 1170   .ECO PUSH DE ;routine to echo byte loaded back to PC terminal.
 1180   PUSH HL ; store HL
 1190   LD H,D:LD L,E ; put address held in DE into HL. 
 1200   PUSH AF
 1210   LD A,(HL) ; load last transfered byte into A reg.
 1220   CALL H_PRINT ; routine to serial output A reg. vallue.
 1230   POP AF
 1240   POP HL ; restore HL value.
 1250   POP DE
 1260   RET
 1270   .RECEIVE PUSH AF ; routine to check for new byte in 8251 USART.
 1280   .CHK IN A,(&11)
 1290   BIT 1,A ; bit 1=1 if fresh byte received.
 1300   JR Z, CHK ; if bit 1=0 go back for new byte
 1310   POP AF
 1320   RET
 1330   .RTS_ON PUSH AF ; hardware handshacking routine. 
 1340   LD A,&27 ; bits 0,1,4 and 5 set. bit 5 is request to send enabled.
 1350   OUT (&11),A ; out A to 8521A reg.
 1360   POP AF
 1370   RET
 1380   .RTS_OFF PUSH AF ; hardware handshaking routine to hold serial out put from PC.
 1390   LD A,&07 ; bits 0,1,2 set and bit 5 reset to 0
 1400   OUT (&11),A ;out A to 8521A reg.
 1410   POP AF
 1420   RET
 1430   .END2 POP HL
 1440   .INEND CALL CHK_IN
 1450   POP HL ; restore as jumped out of loop.
 1460   POP DE; restore as jumped out of loop.
 1470   POP AF; restore as jumped out of loop.
 1480   LD A,64; load A  ascii "@"
 1490   CALL SEND; send to pc terminal to denote download complete.
 1500   LD HL,&0100 ; 
 1510   LD (RN),HL ; reset load start address
 1520   .LEP JP &0100 ; jump to run com prog.-change to hex 0000 to reboot and not run.
 1530   RET
 1540   .H_PRINT PUSH AF ; routine to turn real byte into two hex aascii bytes.
 1550   AND &F0 ; isolates first digit.
 1560   RRA ; move this
 1570   RRA ; digit to
 1580   RRA ; its proper position
 1590   RRA ; in A reg.
 1600   ADD A,&30 ; change to ascii character.
 1610   CP &3A ; is digit between A and FOR
 1620     JR C,HP_H ;
 1630     ADD A,07 ; change to correct sybol if so.
 1640     .HP_H CALL SEND ; serial output byte.
 1650     POP AF ; retrieve original value AND
 1660     AND &0F ; isolate second digit.
 1670     ADD A,&30 ; change to ascii value for character.
 1680     CP &3A ;
 1690     JR C,HP_L
 1700     ADD A,07 ; change to correct hex symbol.
 1710     .HP_L CALL SEND ; serial output AND
 1720     RET
 1730     RET
 1740     .SEND PUSH AF ; store A value
 1750     .REP IN A,(&11)) ; read 8251A usart reg.
 1760     BIT 0,A ; bit 0=1 if new byte ready to send.
 1770     JR Z  REP ; jump back if byte not ready.
 1780     POP AF ; restore A
 1790     OUT (&10),A ; serial output A
 1800     RET
 1810     ]
 1820     RETURN
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