This is a continuation of an earlier article about ZX Spectrum loaders. Hold on to your hats and get your calculators ready, we are going downhill! (Part 1, Part 2)
Last time I finished up stating that next time we’ll need to count and weigh each and every processor tick. This time, our closest ally will be a waiting loop in a routine LD_EDGE_1. Let’s recall that routine:
LD_EDGE_2:
CALL LD_EDGE_1 ;calling, in fact, LD_EDGE_1 once more
RET NC ;return if error
LD_EDGE_1:
LD A,$16 ;7T
LD_DELAY:
DEC A ;4T
JR NZ,LD_DELAY ;12T / 7T
AND A ;4T
LD_SAMPLE:
Do you see it there in LD_DELAY? Yes? So that’s it right there! It takes 7T + 21*(4T+12T) + (4T+7T) = 354T, which is quite a lot of ticks for our purposes. Which purposes, you ask? Well, mostly likely a counter for how much data is remaining to be loaded.
Graphical indicator
In my text game Poradce (The Consultant) I used, besides for some scary flashing, some kind of a “thermometer” that showed how much remains to be loaded. It was that little something on the left side of the screen…
This effect is simpler than you might have expected. The length of the column is almost exactly “file length / 512” (I say “almost exactly” because I had painted it a little shorter…) So I’ll take the upper byte of remaining number of bytes (which is in register pair DE), divide it by two, add offset from the bottom of the screen, convert the coordinate to an address on the screen and mask the byte with value %11100111 – therefore everything else remains except for just two points in the middle, which, coincidentaly, exactly represent our “thermometer” and they get overwritten. To recalculate, I even use a routine PIXEL-ADD ($22AA) from Spectrum’s ROM, which takes the coordinates in B and C (the same coordinate system the PLOT has) and calculates an address on the screen (HL) and a mask of the point (A).
LD_EDGE_2:
CALL LD_EDGE_1
RET NC
LD_EDGE_1:
JP LD_OWN
LD_BACK:
LD A,03 ;7T
LD_DELAY:
DEC A ;4T
JR NZ,LD_DELAY ;12T/7T
;7T + 2*(4+12) + (4+7) = 50T
AND A
LD_SAMPLE:
INC B
RET Z
LD A,7f
IN A,(fe)
RRA
RET NC
XOR C
AND 20
JR Z,LD_SAMPLE
LD A,C
CPL
LD C,A
LD A,06
RRCA
AND 07
OR 08
OUT (fe),A
SCF
RET
LD_OWN:
PUSH DE ;11T
PUSH HL ;11T
PUSH BC ;11T
PUSH AF ;11T
LD B,D ;4T
SRL B ;8T
NOP ;4T
INC B ;4T
INC B ;4T
LD C,00 ;7T
CALL 22aa ;17T + 132T routine
LD A,(HL) ;7T
AND e7 ;7T
LD (HL),A ;7T
POP AF ;10T
POP BC ;10T
POP HL ;10T
POP DE ;10T
JP LD_BACK ;10T
As you can see, I interfered with the timing loop. At the beginning I popped out into my own routine which operates that effect (it is 305T with that diversion) and after returning back I still have enough time, so I’ll wait another 50T, which translates to 355T, which it is pretty much exactly our magic number!
Numeric indicator
If you rather want to show a number instead of some dwindling column, things get more difficult. Each digit must in fact be drawn on the screen, which means eight writes for each digit. And for a three-digit counter this is quite a lot of time, it won’t fit into 354T. So you need to chop the algorithm into parts that fit within this time limit and call them in sequence. The second set of registers and index register IY will be your invaluable tool for this.
Games from Hewson and Czech programs from Universum (I think) had some very nice counters, they used their own font and they also shown fliping digits effect. In another text game I used just a simple counter of “the number of bytes / 64”, which for 48kB block still fits into three digits. At the beginning I prepared the desired digits (in decimal!) into registers D and E (resp. into the mirror ones):
PUSH DE
EXX
POP HL
LD DE,00
LD BC,$40
LD_DIV:
AND A
SBC HL,BC
JR C,b0be
LD A,E
ADD A,01
DAA
LD E,A
LD A,D
ADC A,00
DAA
LD D,A
JR LD_DIV
LD_DIV2:
LD H,3d
LD BC,4001
EXX
LD IY, LD_CHARS ; coming up next...
This effect did not take place directly in LD_EDGE but in LD_8_BITS instead. However, LD_EDGE has been modified so as to use significantly different timing values during loading:
LD B,b0
LD L,01
LD_8_BITS:
CALL LD_EDGE_2M
RET NC
LD A,d4
CP B
RL L
LD B,b0
JP NC,LD_LONGWAY
LD A,H
XOR L
LD H,A
;... the rest of it is normal...
;LD_EDGE_2M : 468 + 58 * B
;shortened by 462T
LD_EDGE_2M:
CALL LD_EDGE_1M
RET NC
LD A,10
DEC A
JR NZ,$-1 ; 254T
LD_EDGE_1M:
AND A
INC B
RET Z
LD A,7f
IN A,(fe)
RRA
XOR C
AND 20
JR Z,b15b
LD A,C
CPL
LD C,A
AND 04
OR 08
OUT (fe),A
SCF
RET
The effect ifself then played out as follows:
LD_LONGWAY:
EXX
DEC C
JP Z,LD_SUB1
JP (IY)
LD_RETHERE:
POP IY
EXX
JP LD_8_BITS
LD_SUB1:
LD C,07
DEC B
JP Z,LD_SUB2
LD A,04
DEC A
JR NZ,b1a9 ;wait 59T
EXX
JP LD_8_BITS
LD_SUB2:
LD A,E
SUB 01
DAA
LD E,A
LD A,D
SBC A,B ;in B there is 0
DAA
LD D,A
LD B,$40
LD IY,LD_CHARS
LD HL,$3d00
EXX
JP LD_8_BITS
;1st digit
LD_CHARS:
LD A,E
ADD A,A
ADD A,A
ADD A,A
OR $81
LD L,A
LD A,(HL)
LD (50fd),A
CALL LD_RETHERE
INC L
LD A,(HL)
LD (51fd),A
INC L
LD A,(HL)
LD (52fd),A
CALL LD_RETHERE
INC L
LD A,(HL)
LD (53fd),A
INC L
LD A,(HL)
LD (54fd),A
CALL LD_RETHERE
INC L
LD A,(HL)
LD (55fd),A
INC L
LD A,(HL)
LD (56fd),A
CALL LD_RETHERE
;2nd digit
LD A,E
AND $f0
RRA
OR $81
LD L,A
LD A,(HL)
LD (50fc),A
CALL LD_RETHERE
INC L
LD A,(HL)
LD (51fc),A
INC L
LD A,(HL)
LD (52fc),A
CALL LD_RETHERE
INC L
LD A,(HL)
LD (53fc),A
INC L
LD A,(HL)
LD (54fc),A
CALL LD_RETHERE
INC L
LD A,(HL)
LD (55fc),A
INC L
LD A,(HL)
LD (56fc),A
CALL LD_RETHERE
;3rd digit
LD A,D
ADD A,A
ADD A,A
ADD A,A
OR $81
LD L,A
LD A,(HL)
LD (50fb),A
CALL LD_RETHERE
INC L
LD A,(HL)
LD (51fb),A
INC L
LD A,(HL)
LD (52fb),A
CALL LD_RETHERE
INC L
LD A,(HL)
LD (53fb),A
INC L
LD A,(HL)
LD (54fb),A
CALL LD_RETHERE
INC L
LD A,(HL)
LD (55fb),A
INC L
LD A,(HL)
LD (56fb),A
LD (56fb),A
NOP
LD IY,LD_CHARS
EXX
JP LD_8_BITS
This, of course, deserves a few explanatory notes:
Registers DE contain the counter itself, stored in BCD coding. The register C contains a bits counter, register B contains a bytes counter. Once they calculate down to zero, the counter gets decreased by 1, the result gets adjusted by DAA instruction and prepared for the actual printing of characters. HL holds the value of $3D00, which coincidentally is an address in the ROM where numbers are stored, and IY holds an address of the routine LD_CHARS, which displays the digits.
When you chop the routine into pieces, you are left with two options. You either edit the code and rewrite the address where you need to jump next, or you store the address somehow. Here it is in the IY register. By using a simple trick CALL LD_RETHERE (as in RETurn HERE) you go back to LD_8_BITS, while the return address gets into IY, so that during the next call the JP (IY) will be directed to the next piece. Note that printing of characters is chopped into small pieces by calling LD_RETHERE.
Time indicator and more
Calculating remaining time is more complicated than counting bytes. You either have to count every bit differently (a one bit is twice as long as a zero bit), or use an interrupt (yes, interrupt in loader!)
I was looking for an example of the first approach, but before I could comment on it, Busy called me and said that he had found his Overscan loader source code, asking me if I want to publish it. So here we go, with Busy’s courtesy, Overscan loader!
(Time calculation and graphical effects are included!)
And here is the source code with Busy’s comments (Thanks!) Because it is a bit long, I shall say my goodbyes right now and wish you good luck in your own experiments.
5b00 *a
5b00 *s
5b00 ;===============================================================;
5b00 ;== Version 16 == Loader for Overscan == 12.08.1991 Busy soft ==;
5b00 ;===============================================================;
5b00 znaky = #8800 modifiet charset
5b00 org #8200,0
8200 f3 p di
8201 310082 ld sp,p
8204 fd217f00 ld iy,#7f timers init for time and auto kitt
8208 210080 ld hl,#8000 IM2 vector init
820b 110180 ld de,#8001
820e 011001 ld bc,#0110
8211 3681 ld (hl),#81
8213 edb0 ldir
8215 212183 ld hl,rut relocation of operation routine IM2
8218 118181 ld de,#8181
821b 010800 ld bc,load-rut
821e edb0 ldir
8220 067f i ld b,#7f
8222 216711 ld hl,#1167
8225 11d685 ld de,k
8228 d5 push de
8229 7e ll14 ld a,(hl) random memory inserts
822a ad xor l (to fool an enemy)
822b 12 ld (de),a
822c 02 ld (bc),a
822d a9 xor c
822e 0b dec bc
822f 02 ld (bc),a
8230 0b dec bc
8231 13 inc de
8232 2b dec hl
8233 7c ld a,h
8234 b5 or l
8235 20f2 jr nz,ll14
8237 e1 pop hl
8238 012a7a ld bc,-k
823b edb0 ldir
823d 3e80 rst ld a,#80 IM2 launch
823f ed47 ld i,a
8241 ed5e im2
8243 fb ei
8244 cd0c85 call zn charset conversion
8247 3e48 ld a,#48
8249 32b784 ld (n20+2),a
824c 210040 ld hl,#4000 screen init
824f 110140 ld de,#4001
8252 010018 ld bc,#1800
8255 71 ld (hl),c
8256 edb0 ldir
8258 010603 ld bc,#0306
825b 71 ld (hl),c
825c edb0 ldir
825e 21a341 o ld hl,#41a3 squares under kitt effect
8261 0e06 ld c,#06
8263 061a ll11 ld b,#1a
8265 e5 push hl
8266 367e ll10 ld (hl),#7e
8268 2c inc l
8269 10fb djnz ll10
826b e1 pop hl
826c 24 inc h
826d 0d dec c
826e 20f3 jr nz,ll11
8270 210059 ld hl,#5900 red frame in the middle
8273 011208 ld bc,#0812
8276 5d ld e,l
8277 73 ll12 ld (hl),e
8278 2c inc l
8279 71 ld (hl),c
827a 7d ld a,l
827b c61d add a,#1d
827d 6f ld l,a
827e 71 ld (hl),c
827f 2c inc l
8280 73 ld (hl),e
8281 2c inc l
8282 10f3 djnz ll12
8284 21e15a ld hl,#5ae1
8287 1e44 ld e,#44
8289 cd0083 call sap
828c 21e158 ld hl,#58e1
828f cdfe82 call pas
8292 21015a ld hl,#5a01
8295 cdfe82 call pas
8298 215f85 ld hl,firma texts printout
829b cd0783 call text
829e 217685 ld hl,demo
82a1 cd0783 call text
82a4 219185 ld hl,loatim
82a7 cd0783 call text
82aa cd2983 call load calling the loader
82ad 08 ex af,af
82ae af xor a
82af cdf884 call out Border 0
82b2 08 ex af,af
82b3 3839 jr c,ok if we loaded a block correctly, then jump
82b5 af error xor a if error during loading
82b6 210048 ld hl,#4800 then show message
82b9 77 ll13 ld (hl),a
82ba 23 inc hl
82bb cb64 bit 4,h
82bd 28fa jr z,ll13
82bf 112548 ld de,#4825
82c2 212515 ld hl,#1525
82c5 cd0b83 call txt
82c8 21d285 ld hl,krik
82cb cd0b83 call txt
82ce 21a585 ld hl,rew
82d1 cd0783 call text
82d4 21b785 ld hl,reload
82d7 cd0783 call text
82da af xor a
82db 32b784 ld (n20+2),a
82de 06ff press ld b,#ff waiting for keypress
82e0 cdcf83 call mmm we call loader during waiting
82e3 af xor a so our effects still run
82e4 dbfe in a,(#fe)
82e6 f6e0 or #e0
82e8 3c inc a
82e9 28f3 jr z,press
82eb c33d82 jp rst
82ee
82ee 210058 ok ld hl,#5800 if we loaded a block correctly
82f1 110158 ld de,#5801 erase all attributes
82f4 0603 ld b,#03
82f6 edb0 ldir
82f8 cde6c3 call 50150 demo decompression
82fb c376e9 jp 59766 demo launch
82fe
82fe 1e12 pas ld e,#12 some help subroutines
8300 061e sap ld b,#1e for frame drawing
8302 73 pp1 ld (hl),e
8303 2c inc l
8304 10fc djnz pp1
8306 c9 ret
8307
8307 5e text ld e,(hl) text printout
8308 23 inc hl HL = text address
8309 56 ld d,(hl) DE = text position on screen
830a 23 inc hl
830b e5 txt push hl
830c d5 push de
830d 6e ld l,(hl)
830e 2688 ld h,>znaky
8310 0608 ld b,#08
8312 7e xtx ld a,(hl) print of one character
8313 12 ld (de),a
8314 14 inc d
8315 24 inc h
8316 10fa djnz xtx
8318 d1 pop de
8319 e1 pop hl
831a 1c inc e
831b cb7e bit 7,(hl) text ends with char with set bit7=1
831d 23 inc hl
831e 28eb jr z,txt
8320 c9 ret
8321
8321 08 rut ex af,af routine from interrupt
8322 fd24 inc yh YH = timer for kitt effect
8324 fd2c inc yl YL = timer for counting and time printing
8326 08 ex af,af
8327 fb ei
8328 c9 ret
8329
8329 af load xor a THIS IS WHERE LOADER BEGINS!!
832a cdf884 call out
832d 211f40 rohy ld hl,#401f drawing of cut off corners
8330 11ff57 ld de,#57ff
8333 7b ld a,e
8334 77 ld (hl),a
8335 12 ld (de),a
8336 d9 exx
8337 010207 ld bc,#0702
833a 210040 ld hl,#4000
833d 11e057 ld de,#57e0
8340 77 ld (hl),a
8341 12 ld (de),a
8342 7e rr1 ld a,(hl)
8343 24 inc h
8344 15 dec d
8345 cb27 sla a
8347 77 ld (hl),a
8348 12 ld (de),a
8349 d9 exx
834a 7e ld a,(hl)
834b 24 inc h
834c 15 dec d
834d cb3f srl a
834f 77 ld (hl),a
8350 12 ld (de),a
8351 d9 exx
8352 10ee djnz rr1
8354 nnn
8354 3ef8 rrr ld a,#f8 catching the leader tone
8356 32f484 ld (xor+1),a
8359 2600 ld h,#00
835b 06ff djnz ld b,#ff
835d cdcf83 call mmm
8360 25 dec h
8361 20f8 jr nz,djnz
8363 cdcf83 call mmm
8366 30ec jr nc,nnn
8368 cdcb83 call ppp
836b 30e7 jr nc,nnn
836d 069c sss ld b,#9c
836f cdcb83 call ppp
8372 30e0 jr nc,nnn
8374 3ec6 ld a,#c6
8376 b8 cp b
8377 30db jr nc,rrr
8379 24 inc h
837a 20f1 jr nz,sss
837c 3efc ld a,#fc
837e 32f484 ld (xor+1),a
8381 06c9 ttt ld b,#c9
8383 cdcf83 call mmm
8386 30cc jr nc,nnn
8388 78 ld a,b
8389 fed4 cp #d4
838b 30f4 jr nc,ttt
838d cdcf83 call mmm
8390 d0 ret nc
8391 79 ld a,c leader and sync-pulse OK, we can start loading
8392 ee03 xor #03
8394 4f ld c,a
8395 cdb583 call byte flagbyte Load
8398 d0 ret nc
8399
8399 dd21e6c3 loa ld ix,50150 demo bytes loading loop
839d 116a24 ld de,9322
83a0 ; ld ix,#4000 during testing of effects in loader
83a0 ; ld de,#1b00 the block was loaded onto the screen
83a0 cdb583 loa1 call byte
83a3 d0 ret nc
83a4 dd7500 ld (ix+#00),l
83a7 dd23 inc ix
83a9 1b dec de
83aa 7a ld a,d
83ab b3 or e
83ac 20f2 jr nz,loa1
83ae cdb583 call byte load parity
83b1 d0 ret nc
83b2 fe01 cp #01
83b4 c9 ret
83b5
83b5 06b2 byte ld b,#b2 Load of one byte
83b7 2e01 ld l,#01
83b9 cdcb83 loa9 call ppp
83bc d0 ret nc
83bd 3ecb kk ld a,#cb
83bf b8 cp b
83c0 cb15 rl l
83c2 06b0 ld b,#b0
83c4 30f3 jr nc,loa9
83c6 7c ld a,h
83c7 ad xor l
83c8 67 ld h,a
83c9 37 scf
83ca c9 ret
83cb
83cb cdcf83 ppp call mmm Load of one byte
83ce d0 ret nc
83cf d9 mmm exx load of one halfperiod
83d0 c3 db #c3 there are my special subroutines instead of wating loop
83d1 ec83 skok dw n1 jump to part of code to execute next
83d3
83d3 7e n1sub ld a,(hl) /0
83d4 81 add a,c time value recalcullation
83d5 fe0a cp #0a
83d7 0e00 ld c,#00
83d9 3802 jr c,n1aa
83db 0c inc c
83dc af xor a
83dd 77 n1aa ld (hl),a
83de 23 inc hl \50
83df 7e ld a,(hl)
83e0 81 add a,c
83e1 fe06 cp #06
83e3 0e00 ld c,#00
83e5 3802 jr c,n1bb
83e7 0c inc c
83e8 af xor a
83e9 77 n1bb ld (hl),a
83ea 23 inc hl \100
83eb c9 ret \110+call=117
83ec
83ec fd7d n1 ld a,yl
83ee fe33 cp 51 \29
83f0 3866 jr c,n10 Test if a second has passed
83f2 0e01 ld c,#01 so that we could draw another time value
83f4 fd7d ld a,yl
83f6 d632 sub 50
83f8 fd6f ld yl,a
83fa 215a85 ld hl,cas \76
83fd cdd383 call n1sub
8400 3e04 ld a,#04
8402 110784 ld de,n3
8405 181a jr jpde \222 +/-
8407
8407 23 n3 inc hl every second we also change
8408 cdd383 call n1sub an efect in middle third
840b ed5f ld a,r
840d 32b984 ld (udaj+1),a
8410 3a5b85 ld a,(cas+1)
8413 0f rrca
8414 9f sbc a,a
8415 e60f and #0f
8417 f607 or #07
8419 32cc84 ld (rot),a
841c 3e05 ld a,#05
841e 112a84 ld de,n2
8421 ed53d183 jpde ld (skok),de
8425 1ef9 ld e,#f9
8427 c3e084 jp wait \222 +/-
842a
842a 2b n2 dec hl
842b cb7e bit 7,(hl) \32
842d 2808 jr z,n2aa prepare to print one character
842f 3e0e ld a,14
8431 01ec83 ld bc,n1
8434 c3dc84 jp buduci
8437 e5 n2aa push hl
8438 6e ld l,(hl)
8439 2688 ld h,>znaky
843b 1650 ld d,#50
843d 0602 ld b,#02 /2*88=202
843f 7e dd1 ld a,(hl) print of one character
8440 12 ld (de),a
8441 24 inc h
8442 14 inc d
8443 7e ld a,(hl)
8444 12 ld (de),a
8445 24 inc h
8446 14 inc d
8447 7e ld a,(hl)
8448 12 ld (de),a
8449 24 inc h
844a 14 inc d
844b 7e ld a,(hl)
844c 12 ld (de),a
844d 24 inc h
844e 14 inc d
844f 10ee djnz dd1
8451 1c inc e
8452 e1 pop hl
8453 3e01 ld a,#01 \299
8455 c3e084 jp wait
8458
8458 fd7c n10 ld a,yh Auto-Kitt effect
845a fe02 cp #02 \56
845c 3857 jr c,n20 test if we can go into another phase
845e c3 db #c3
845f 9584 jump dw n12 \73
8461
8461 21a358 n11 ld hl,#58a3
8464 3647 ld (hl),#47
8466 2c incdec inc l
8467 7d ld a,l
8468 326284 ld (n11+1),a
846b 216684 ld hl,incdec \124
846e febc cp #bc
8470 3f ccf
8471 3802 jr c,iidd
8473 fea4 cp #a4
8475 9f iidd sbc a,a \151
8476 e601 and #01
8478 ae xor (hl)
8479 77 ld (hl),a
847a 218484 ld hl,jr+1
847d 3e03 ld a,#03
847f ae xor (hl)
8480 77 ld (hl),a
8481 3ea2 ld a,#a2 \210
8483 1803 jr jr #03
8485 329684 ld (n12+1),a
8488 fd2600 ld yh,#00
848b 3e02 ld a,#02
848d 219584 ld hl,n12
8490 225f84 buduce ld (jump),hl
8493 184b jr wait \267
8495
8495 216458 n12 ld hl,#5864 \73
8498 7d ld a,l
8499 febc cp #bc \94
849b 3011 jr nc,n12bb
849d 014104 ld bc,#0441 \111
84a0 7e n12aa ld a,(hl) /47
84a1 b9 cp c
84a2 3801 jr c,#01
84a4 3d dec a
84a5 77 ld (hl),a
84a6 2c inc l
84a7 10f7 djnz n12aa \4*47=188
84a9 229684 ld (n12+1),hl
84ac 1835 jr end
84ae
84ae 3e08 n12bb ld a,#08
84b0 216184 ld hl,n11
84b3 18db jr buduce /\174
84b5
84b5 210048 n20 ld hl,#4800 filling the middle third of the screen
84b8 3e33 udaj ld a,#33 \82
84ba 772c772c dw #2c77,#2c77 8*[INC C : LD (HL),A]
84be 772c772c dw #2c77,#2c77
84c2 772c772c dw #2c77,#2c77 8*11=88
84c6 772c772c dw #2c77,#2c77 \
84ca 2002 jr nz,n21 /
84cc 0f rot rrca
84cd 24 inc h
84ce cba4 n21 res 4,h
84d0 cbdc set 3,h
84d2 22b684 ld (n20+1),hl
84d5 32b984 ld (udaj+1),a
84d8 3e03 ld a,3
84da 1804 jr wait \68
84dc
84dc ed43d183 buduci ld (skok),bc setting of what part of code to call next
84e0 3d wait dec a
84e1 20fd jr nz,wait
84e3 d9 end exx all code parts last 200 cycles (+/- give or take)
84e4 a7 zzz and a end of my special subroutines
84e5 04 l222 inc b
84e6 c8 ret z
84e7 3eff ld a,#ff #FF instead of #7F does not respond to SPACEBAR
84e9 dbfe in a,(#fe)
84eb 1f rra
84ec d0 ret nc
84ed a9 xor c
84ee e620 and #20
84f0 28f3 jr z,l222
84f2 79 ld a,c
84f3 eefc xor xor #fc #FC instead of CPL makes prettier colours
84f5 4f ld c,a red-yellow boot tone and blue-blue bytes
84f6 e607 and #07
84f8 320058 out ld (#5800),a +52
84fb 321f58 ld (#581f),a setting of corner attributes
84fe f608 or #08
8500 d3fe out (#fe),a
8502 e607 and #07
8504 32e05a ld (#5ae0),a
8507 32ff5a ld (#5aff),a
850a 37 scf
850b c9 ret
850c
850c 110088 zn ld de,znaky charset conversion
850f d5 ll1 push de from ROM font makes contures
8510 7b ld a,e also font gets reorganized so that
8511 fe20 cp ' ' print routines can run faster
8513 3002 jr nc,#02
8515 c630 add a,'0'
8517 87 add a,a
8518 6f ld l,a
8519 260f ld h,#0f
851b 29 add hl,hl
851c 29 add hl,hl
851d cd4985 call read
8520 4f ld c,a
8521 23 inc hl
8522 cd5085 call write
8525 0606 ld b,#06
8527 cd4985 ll2 call read
852a 4f ld c,a
852b 2b dec hl
852c cd4985 call read
852f b1 or c
8530 4f ld c,a
8531 23 inc hl
8532 23 inc hl
8533 cd5085 call write
8536 10ef djnz ll2
8538 cd4985 call read
853b 4f ld c,a
853c 2b dec hl
853d cd4985 call read
8540 23 inc hl
8541 cd5485 call rit
8544 d1 pop de
8545 1c inc e
8546 20c7 jr nz,ll1
8548 c9 ret
8549
8549 7e read ld a,(hl)
854a 0f rrca
854b 0f rrca
854c b6 or (hl)
854d 07 rlca
854e b6 or (hl)
854f c9 ret
8550
8550 cd4985 write call read
8553 2b dec hl
8554 b1 rit or c
8555 ae xor (hl)
8556 12 ld (de),a
8557 23 inc hl
8558 14 inc d
8559 c9 ret
855a 00000a00 cas db 0,0,10,0,0 Buffer for time value
855f 4550 firma dw #5045
8561 42757379 db 'Busy software '
6
2
856f 70726573 db 'presen','t'+#80
8576 8350 demo dw #5083
8578 3e3e3e20 db '>>> THE OVER'
0
8584 5343414e db 'SCAN DEMO <<'
d
8590 bc db '<'+#80
8591 e250 loatim dw #50e2
8593 4c6f6164 db 'Loading'
859a 20636361 db ' cca 1 min'
d
85a4 ae db '.'+#80
85a5 8848 rew dw #4888
85a7 52657769 db 'Rewing the tape'
4
4
85b6 ac db ','+#80
85b7 c448 reload dw #48c4
85b9 70726573 db 'press any key '
e
5
85c7 616e6420 db 'and reload'
f
85d1 ae db '.'+#80
85d2 202121a1 krik db ' !!','!'+#80
85d6 k
85d6 l = k-p label "l" will be total code length
85d6
85d6 org #6000,0 next routines have no use
6000 f3 mrs di they were debug routines
6001 ed56 im1
6003 af xor a
6004 ed47 ld i,a
6006 c3b3f4 jp #f4b3 jump into MRS
6009
6009 cd0c85 zs call zn Test of conversion of charset
600c 210088 ld hl,znaky printing of all characters
600f 110040 ld de,#4000 on the screen
6012 010008 ld bc,#0800
6015 edb0 ldir
6017 c9 ret
6018
6018 3e0c poke ld a,12 sets testing im2 vector into ROM
601a d317 out (23),a (Outs for writing into ROM on MB01)
601c 218181 ld hl,#8181
601f 22ff3a ld (#3aff),hl
6022 3e04 ld a,4
6024 d317 out (23),a
6026 c9 ret
6027 end
(Translated by Ondřej Ficek)