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F/+CIRC1
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.
| Tape/disk: | Home » Personal collection » Acorn ADFS disks » Electron_User_Group » EUG_31.ADF |
| Filename: | F/+CIRC1 |
| Read OK: | ✔ |
| File size: | 0DE3 bytes |
| Load address: | 2B204556 |
| Exec address: | 43524943 |
File contents
�..>......*.......*.......*.......*.......*.......*.......*.......*.......*.<
This is the second part of my "buildit" series, where part one brought you
he handy 16k Eprom Emulator.
This time,I present a "BBC Slower owner".
As we all know the BBC is very fast in all that it does - but some things
are just better in slow motion.
ADVANTAGES: Watch games in slow motion See how the OS does things slowly
No software required so requires no RAM or ROM sockets Does not hog the
user port
DISADVANTAGES: Loss of 1MHz bus socket Requires external power source he
circuit - the main circuit is based around the easy to use (and cheap!)
555 timer chip.Other oscillators, such as push/pull transistors could have
been used, but the 555 gives most control over the time high to time low
ratio.
The values chosen in the diagram (see attached) are only rough values,
they happened to be the parts that I had in my bits 'n' bobs drawer at the
time. In general any NPN transistor will do, only its switching properties
are required. Because of the way a 555 charges its timing capacitor, the
low time is always shorter than the high time.This is not what I wanted,
so the transistor also acts to invert the 555's output. It also means that
I present EITHER a low pulse OR a high impedance to the IRQ line and NEVER
a logic high. This is required as the IRQ line is wire-ORed to all the
other IRQ sources. The ratio of resistances should be kept approximately
the same otherwise he ratio of time high to time low will alter and the
effect will be spoilt.
I suggest trying a logarithmic potentiometer so that all the action
doesn't happen in the first two or three degrees of turning the knob!
How it works
With the pot fully rotated there is zero resistance between its pinouts.
So the output of the 555 is permanently LOW and so the NPN transistor is
off. Increasing the pot's resistance makes he 555 oscillate, and the high
period is proportional to the pot's resistance and so the transistor is on
for longer and longer periods at a time. Then on, the transistor spikes
nIRQ to round and causes an interrupt. As the interrupt comes from the
1MHz bus, the OS isn't interested in it and passes it to the paged ROMs,
who also ignore it and send it through IRQ2V whereupon it returns to the
OS which simply does an RTI instruction. All of this handling and polling
takes a finite amount of time, so if the IRQ occurs often enough then the
BBC doesn't have time to do its other tasks such as updating the screen,
or running the game that is in memory.
Originally, my design ran at higher frequency, spiking nIRQ low for
shorter times, but more often. This seemed to have little effect on the
BBC. Clearly it's just too fast!
Now the interrupts come long and frequently - giving little time for
foreground activities. Try this - two things of particular amusement are
changing to MODE0 and typing COLOUR 29 then CLS. You can watch exactly how
he OS sets all the 20k of locations to 255. Also, if you have it, play
Hopper at low speed - you can hear the individual notes in the envelopes
used to create the tune and sound effects.
Warning - do not use this with the "SNAPIT" ROM that I sent a few issues
back as it monitors the 1MHz bus interrupt line and starts the disk drive
up every time nIRQ goes low! If you feel the need to press BREAK with the
slower downer plugged in then make sure you turn the pot down to zero
resistance otherwise an IRQ occurs during reset. Nasty! let me know how
you get on...
Robert Sprowson.
�
00000000 81 2e 2e 3e 2e 2e 2e 2e 2e 2e 2a 2e 2e 2e 2e 2e |...>......*.....| 00000010 2e 2e 2a 2e 2e 2e 2e 2e 2e 2e 2a 2e 2e 2e 2e 2e |..*.......*.....| * 00000040 2e 2e 2a 2e 2e 2e 2e 2e 2e 2e 2a 2e 3c 0d 54 68 |..*.......*.<.Th| 00000050 69 73 20 69 73 20 74 68 65 20 73 65 63 6f 6e 64 |is is the second| 00000060 20 70 61 72 74 20 6f 66 20 6d 79 20 22 62 75 69 | part of my "bui| 00000070 6c 64 69 74 22 20 73 65 72 69 65 73 2c 20 77 68 |ldit" series, wh| 00000080 65 72 65 20 70 61 72 74 20 6f 6e 65 20 62 72 6f |ere part one bro| 00000090 75 67 68 74 20 79 6f 75 0d 68 65 20 68 61 6e 64 |ught you.he hand| 000000a0 79 20 31 36 6b 20 45 70 72 6f 6d 20 45 6d 75 6c |y 16k Eprom Emul| 000000b0 61 74 6f 72 2e 20 0d 0d 54 68 69 73 20 74 69 6d |ator. ..This tim| 000000c0 65 2c 49 20 70 72 65 73 65 6e 74 20 61 20 22 42 |e,I present a "B| 000000d0 42 43 20 53 6c 6f 77 65 72 20 6f 77 6e 65 72 22 |BC Slower owner"| 000000e0 2e 0d 0d 41 73 20 77 65 20 61 6c 6c 20 6b 6e 6f |...As we all kno| 000000f0 77 20 74 68 65 20 42 42 43 20 69 73 20 76 65 72 |w the BBC is ver| 00000100 79 20 66 61 73 74 20 69 6e 20 61 6c 6c 20 74 68 |y fast in all th| 00000110 61 74 20 69 74 20 64 6f 65 73 20 2d 20 62 75 74 |at it does - but| 00000120 20 73 6f 6d 65 20 74 68 69 6e 67 73 0d 61 72 65 | some things.are| 00000130 20 6a 75 73 74 20 62 65 74 74 65 72 20 69 6e 20 | just better in | 00000140 73 6c 6f 77 20 6d 6f 74 69 6f 6e 2e 20 0d 0d 41 |slow motion. ..A| 00000150 44 56 41 4e 54 41 47 45 53 3a 20 57 61 74 63 68 |DVANTAGES: Watch| 00000160 20 67 61 6d 65 73 20 69 6e 20 73 6c 6f 77 20 6d | games in slow m| 00000170 6f 74 69 6f 6e 20 53 65 65 20 68 6f 77 20 74 68 |otion See how th| 00000180 65 20 4f 53 20 64 6f 65 73 20 74 68 69 6e 67 73 |e OS does things| 00000190 20 73 6c 6f 77 6c 79 0d 4e 6f 20 73 6f 66 74 77 | slowly.No softw| 000001a0 61 72 65 20 72 65 71 75 69 72 65 64 20 73 6f 20 |are required so | 000001b0 72 65 71 75 69 72 65 73 20 6e 6f 20 20 52 41 4d |requires no RAM| 000001c0 20 6f 72 20 52 4f 4d 20 73 6f 63 6b 65 74 73 20 | or ROM sockets | 000001d0 44 6f 65 73 20 6e 6f 74 20 68 6f 67 20 74 68 65 |Does not hog the| 000001e0 0d 75 73 65 72 20 70 6f 72 74 20 0d 0d 44 49 53 |.user port ..DIS| 000001f0 41 44 56 41 4e 54 41 47 45 53 3a 20 4c 6f 73 73 |ADVANTAGES: Loss| 00000200 20 6f 66 20 31 4d 48 7a 20 62 75 73 20 73 6f 63 | of 1MHz bus soc| 00000210 6b 65 74 20 52 65 71 75 69 72 65 73 20 65 78 74 |ket Requires ext| 00000220 65 72 6e 61 6c 20 70 6f 77 65 72 20 73 6f 75 72 |ernal power sour| 00000230 63 65 20 68 65 0d 63 69 72 63 75 69 74 20 2d 20 |ce he.circuit - | 00000240 74 68 65 20 6d 61 69 6e 20 63 69 72 63 75 69 74 |the main circuit| 00000250 20 69 73 20 62 61 73 65 64 20 61 72 6f 75 6e 64 | is based around| 00000260 20 74 68 65 20 65 61 73 79 20 74 6f 20 75 73 65 | the easy to use| 00000270 20 28 61 6e 64 20 63 68 65 61 70 21 29 0d 35 35 | (and cheap!).55| 00000280 35 20 74 69 6d 65 72 20 63 68 69 70 2e 4f 74 68 |5 timer chip.Oth| 00000290 65 72 20 6f 73 63 69 6c 6c 61 74 6f 72 73 2c 20 |er oscillators, | 000002a0 73 75 63 68 20 61 73 20 70 75 73 68 2f 70 75 6c |such as push/pul| 000002b0 6c 20 74 72 61 6e 73 69 73 74 6f 72 73 20 63 6f |l transistors co| 000002c0 75 6c 64 20 68 61 76 65 0d 62 65 65 6e 20 75 73 |uld have.been us| 000002d0 65 64 2c 20 62 75 74 20 74 68 65 20 35 35 35 20 |ed, but the 555 | 000002e0 67 69 76 65 73 20 6d 6f 73 74 20 63 6f 6e 74 72 |gives most contr| 000002f0 6f 6c 20 6f 76 65 72 20 74 68 65 20 74 69 6d 65 |ol over the time| 00000300 20 68 69 67 68 20 74 6f 20 74 69 6d 65 20 6c 6f | high to time lo| 00000310 77 0d 72 61 74 69 6f 2e 20 0d 0d 54 68 65 20 76 |w.ratio. ..The v| 00000320 61 6c 75 65 73 20 63 68 6f 73 65 6e 20 69 6e 20 |alues chosen in | 00000330 74 68 65 20 64 69 61 67 72 61 6d 20 28 73 65 65 |the diagram (see| 00000340 20 61 74 74 61 63 68 65 64 29 20 61 72 65 20 6f | attached) are o| 00000350 6e 6c 79 20 72 6f 75 67 68 20 76 61 6c 75 65 73 |nly rough values| 00000360 2c 0d 74 68 65 79 20 68 61 70 70 65 6e 65 64 20 |,.they happened | 00000370 74 6f 20 62 65 20 74 68 65 20 70 61 72 74 73 20 |to be the parts | 00000380 74 68 61 74 20 49 20 68 61 64 20 69 6e 20 6d 79 |that I had in my| 00000390 20 62 69 74 73 20 27 6e 27 20 62 6f 62 73 20 64 | bits 'n' bobs d| 000003a0 72 61 77 65 72 20 61 74 20 74 68 65 0d 74 69 6d |rawer at the.tim| 000003b0 65 2e 20 49 6e 20 67 65 6e 65 72 61 6c 20 61 6e |e. In general an| 000003c0 79 20 4e 50 4e 20 74 72 61 6e 73 69 73 74 6f 72 |y NPN transistor| 000003d0 20 77 69 6c 6c 20 64 6f 2c 20 6f 6e 6c 79 20 69 | will do, only i| 000003e0 74 73 20 73 77 69 74 63 68 69 6e 67 20 70 72 6f |ts switching pro| 000003f0 70 65 72 74 69 65 73 0d 61 72 65 20 72 65 71 75 |perties.are requ| 00000400 69 72 65 64 2e 20 42 65 63 61 75 73 65 20 6f 66 |ired. Because of| 00000410 20 74 68 65 20 77 61 79 20 61 20 35 35 35 20 63 | the way a 555 c| 00000420 68 61 72 67 65 73 20 69 74 73 20 74 69 6d 69 6e |harges its timin| 00000430 67 20 63 61 70 61 63 69 74 6f 72 2c 20 74 68 65 |g capacitor, the| 00000440 0d 6c 6f 77 20 74 69 6d 65 20 69 73 20 61 6c 77 |.low time is alw| 00000450 61 79 73 20 73 68 6f 72 74 65 72 20 74 68 61 6e |ays shorter than| 00000460 20 74 68 65 20 68 69 67 68 20 74 69 6d 65 2e 54 | the high time.T| 00000470 68 69 73 20 69 73 20 6e 6f 74 20 77 68 61 74 20 |his is not what | 00000480 49 20 77 61 6e 74 65 64 2c 0d 73 6f 20 74 68 65 |I wanted,.so the| 00000490 20 74 72 61 6e 73 69 73 74 6f 72 20 61 6c 73 6f | transistor also| 000004a0 20 61 63 74 73 20 74 6f 20 69 6e 76 65 72 74 20 | acts to invert | 000004b0 74 68 65 20 35 35 35 27 73 20 6f 75 74 70 75 74 |the 555's output| 000004c0 2e 20 49 74 20 61 6c 73 6f 20 6d 65 61 6e 73 20 |. It also means | 000004d0 74 68 61 74 0d 49 20 70 72 65 73 65 6e 74 20 45 |that.I present E| 000004e0 49 54 48 45 52 20 61 20 6c 6f 77 20 70 75 6c 73 |ITHER a low puls| 000004f0 65 20 4f 52 20 61 20 68 69 67 68 20 69 6d 70 65 |e OR a high impe| 00000500 64 61 6e 63 65 20 74 6f 20 74 68 65 20 49 52 51 |dance to the IRQ| 00000510 20 6c 69 6e 65 20 61 6e 64 20 4e 45 56 45 52 0d | line and NEVER.| 00000520 61 20 6c 6f 67 69 63 20 68 69 67 68 2e 20 54 68 |a logic high. Th| 00000530 69 73 20 69 73 20 72 65 71 75 69 72 65 64 20 61 |is is required a| 00000540 73 20 74 68 65 20 49 52 51 20 6c 69 6e 65 20 69 |s the IRQ line i| 00000550 73 20 77 69 72 65 2d 4f 52 65 64 20 74 6f 20 61 |s wire-ORed to a| 00000560 6c 6c 20 74 68 65 0d 6f 74 68 65 72 20 49 52 51 |ll the.other IRQ| 00000570 20 73 6f 75 72 63 65 73 2e 20 54 68 65 20 72 61 | sources. The ra| 00000580 74 69 6f 20 6f 66 20 72 65 73 69 73 74 61 6e 63 |tio of resistanc| 00000590 65 73 20 73 68 6f 75 6c 64 20 62 65 20 6b 65 70 |es should be kep| 000005a0 74 20 61 70 70 72 6f 78 69 6d 61 74 65 6c 79 0d |t approximately.| 000005b0 74 68 65 20 73 61 6d 65 20 6f 74 68 65 72 77 69 |the same otherwi| 000005c0 73 65 20 68 65 20 72 61 74 69 6f 20 6f 66 20 74 |se he ratio of t| 000005d0 69 6d 65 20 68 69 67 68 20 74 6f 20 74 69 6d 65 |ime high to time| 000005e0 20 6c 6f 77 20 77 69 6c 6c 20 61 6c 74 65 72 20 | low will alter | 000005f0 61 6e 64 20 74 68 65 0d 65 66 66 65 63 74 20 77 |and the.effect w| 00000600 69 6c 6c 20 62 65 20 73 70 6f 69 6c 74 2e 0d 0d |ill be spoilt...| 00000610 49 20 73 75 67 67 65 73 74 20 74 72 79 69 6e 67 |I suggest trying| 00000620 20 61 20 6c 6f 67 61 72 69 74 68 6d 69 63 20 70 | a logarithmic p| 00000630 6f 74 65 6e 74 69 6f 6d 65 74 65 72 20 73 6f 20 |otentiometer so | 00000640 74 68 61 74 20 61 6c 6c 20 74 68 65 20 61 63 74 |that all the act| 00000650 69 6f 6e 0d 64 6f 65 73 6e 27 74 20 68 61 70 70 |ion.doesn't happ| 00000660 65 6e 20 69 6e 20 74 68 65 20 66 69 72 73 74 20 |en in the first | 00000670 74 77 6f 20 6f 72 20 74 68 72 65 65 20 64 65 67 |two or three deg| 00000680 72 65 65 73 20 6f 66 20 74 75 72 6e 69 6e 67 20 |rees of turning | 00000690 74 68 65 20 6b 6e 6f 62 21 0d 0d 20 0b 48 6f 77 |the knob!.. .How| 000006a0 20 69 74 20 77 6f 72 6b 73 0d 57 69 74 68 20 74 | it works.With t| 000006b0 68 65 20 70 6f 74 20 66 75 6c 6c 79 20 72 6f 74 |he pot fully rot| 000006c0 61 74 65 64 20 74 68 65 72 65 20 69 73 20 7a 65 |ated there is ze| 000006d0 72 6f 20 72 65 73 69 73 74 61 6e 63 65 20 62 65 |ro resistance be| 000006e0 74 77 65 65 6e 20 69 74 73 20 70 69 6e 6f 75 74 |tween its pinout| 000006f0 73 2e 0d 53 6f 20 74 68 65 20 6f 75 74 70 75 74 |s..So the output| 00000700 20 6f 66 20 74 68 65 20 35 35 35 20 69 73 20 70 | of the 555 is p| 00000710 65 72 6d 61 6e 65 6e 74 6c 79 20 4c 4f 57 20 61 |ermanently LOW a| 00000720 6e 64 20 73 6f 20 74 68 65 20 4e 50 4e 20 74 72 |nd so the NPN tr| 00000730 61 6e 73 69 73 74 6f 72 20 69 73 0d 6f 66 66 2e |ansistor is.off.| 00000740 20 49 6e 63 72 65 61 73 69 6e 67 20 74 68 65 20 | Increasing the | 00000750 70 6f 74 27 73 20 72 65 73 69 73 74 61 6e 63 65 |pot's resistance| 00000760 20 6d 61 6b 65 73 20 68 65 20 35 35 35 20 6f 73 | makes he 555 os| 00000770 63 69 6c 6c 61 74 65 2c 20 61 6e 64 20 74 68 65 |cillate, and the| 00000780 20 68 69 67 68 0d 70 65 72 69 6f 64 20 69 73 20 | high.period is | 00000790 70 72 6f 70 6f 72 74 69 6f 6e 61 6c 20 74 6f 20 |proportional to | 000007a0 74 68 65 20 70 6f 74 27 73 20 72 65 73 69 73 74 |the pot's resist| 000007b0 61 6e 63 65 20 61 6e 64 20 73 6f 20 74 68 65 20 |ance and so the | 000007c0 74 72 61 6e 73 69 73 74 6f 72 20 69 73 20 6f 6e |transistor is on| 000007d0 0d 66 6f 72 20 6c 6f 6e 67 65 72 20 61 6e 64 20 |.for longer and | 000007e0 6c 6f 6e 67 65 72 20 70 65 72 69 6f 64 73 20 61 |longer periods a| 000007f0 74 20 61 20 74 69 6d 65 2e 20 54 68 65 6e 20 6f |t a time. Then o| 00000800 6e 2c 20 74 68 65 20 74 72 61 6e 73 69 73 74 6f |n, the transisto| 00000810 72 20 73 70 69 6b 65 73 0d 6e 49 52 51 20 74 6f |r spikes.nIRQ to| 00000820 20 72 6f 75 6e 64 20 61 6e 64 20 63 61 75 73 65 | round and cause| 00000830 73 20 61 6e 20 69 6e 74 65 72 72 75 70 74 2e 20 |s an interrupt. | 00000840 41 73 20 74 68 65 20 69 6e 74 65 72 72 75 70 74 |As the interrupt| 00000850 20 63 6f 6d 65 73 20 66 72 6f 6d 20 74 68 65 0d | comes from the.| 00000860 31 4d 48 7a 20 62 75 73 2c 20 74 68 65 20 4f 53 |1MHz bus, the OS| 00000870 20 69 73 6e 27 74 20 69 6e 74 65 72 65 73 74 65 | isn't intereste| 00000880 64 20 69 6e 20 69 74 20 61 6e 64 20 70 61 73 73 |d in it and pass| 00000890 65 73 20 69 74 20 74 6f 20 74 68 65 20 70 61 67 |es it to the pag| 000008a0 65 64 20 52 4f 4d 73 2c 0d 77 68 6f 20 61 6c 73 |ed ROMs,.who als| 000008b0 6f 20 69 67 6e 6f 72 65 20 69 74 20 61 6e 64 20 |o ignore it and | 000008c0 73 65 6e 64 20 69 74 20 74 68 72 6f 75 67 68 20 |send it through | 000008d0 49 52 51 32 56 20 77 68 65 72 65 75 70 6f 6e 20 |IRQ2V whereupon | 000008e0 69 74 20 72 65 74 75 72 6e 73 20 74 6f 20 74 68 |it returns to th| 000008f0 65 0d 4f 53 20 77 68 69 63 68 20 73 69 6d 70 6c |e.OS which simpl| 00000900 79 20 64 6f 65 73 20 61 6e 20 52 54 49 20 69 6e |y does an RTI in| 00000910 73 74 72 75 63 74 69 6f 6e 2e 20 41 6c 6c 20 6f |struction. All o| 00000920 66 20 74 68 69 73 20 68 61 6e 64 6c 69 6e 67 20 |f this handling | 00000930 61 6e 64 20 70 6f 6c 6c 69 6e 67 0d 74 61 6b 65 |and polling.take| 00000940 73 20 61 20 66 69 6e 69 74 65 20 61 6d 6f 75 6e |s a finite amoun| 00000950 74 20 6f 66 20 74 69 6d 65 2c 20 73 6f 20 69 66 |t of time, so if| 00000960 20 74 68 65 20 49 52 51 20 6f 63 63 75 72 73 20 | the IRQ occurs | 00000970 6f 66 74 65 6e 20 65 6e 6f 75 67 68 20 74 68 65 |often enough the| 00000980 6e 20 74 68 65 0d 42 42 43 20 64 6f 65 73 6e 27 |n the.BBC doesn'| 00000990 74 20 68 61 76 65 20 74 69 6d 65 20 74 6f 20 64 |t have time to d| 000009a0 6f 20 69 74 73 20 6f 74 68 65 72 20 74 61 73 6b |o its other task| 000009b0 73 20 73 75 63 68 20 61 73 20 75 70 64 61 74 69 |s such as updati| 000009c0 6e 67 20 74 68 65 20 73 63 72 65 65 6e 2c 0d 6f |ng the screen,.o| 000009d0 72 20 72 75 6e 6e 69 6e 67 20 74 68 65 20 67 61 |r running the ga| 000009e0 6d 65 20 74 68 61 74 20 69 73 20 69 6e 20 6d 65 |me that is in me| 000009f0 6d 6f 72 79 2e 20 0d 0d 4f 72 69 67 69 6e 61 6c |mory. ..Original| 00000a00 6c 79 2c 20 6d 79 20 64 65 73 69 67 6e 20 72 61 |ly, my design ra| 00000a10 6e 20 61 74 20 68 69 67 68 65 72 20 66 72 65 71 |n at higher freq| 00000a20 75 65 6e 63 79 2c 20 73 70 69 6b 69 6e 67 20 6e |uency, spiking n| 00000a30 49 52 51 20 6c 6f 77 20 66 6f 72 0d 73 68 6f 72 |IRQ low for.shor| 00000a40 74 65 72 20 74 69 6d 65 73 2c 20 62 75 74 20 6d |ter times, but m| 00000a50 6f 72 65 20 6f 66 74 65 6e 2e 20 54 68 69 73 20 |ore often. This | 00000a60 73 65 65 6d 65 64 20 74 6f 20 68 61 76 65 20 6c |seemed to have l| 00000a70 69 74 74 6c 65 20 65 66 66 65 63 74 20 6f 6e 20 |ittle effect on | 00000a80 74 68 65 20 0d 42 42 43 2e 20 43 6c 65 61 72 6c |the .BBC. Clearl| 00000a90 79 20 69 74 27 73 20 6a 75 73 74 20 74 6f 6f 20 |y it's just too | 00000aa0 66 61 73 74 21 20 0d 0d 4e 6f 77 20 74 68 65 20 |fast! ..Now the | 00000ab0 69 6e 74 65 72 72 75 70 74 73 20 63 6f 6d 65 20 |interrupts come | 00000ac0 6c 6f 6e 67 20 61 6e 64 20 66 72 65 71 75 65 6e |long and frequen| 00000ad0 74 6c 79 20 2d 20 67 69 76 69 6e 67 20 6c 69 74 |tly - giving lit| 00000ae0 74 6c 65 20 74 69 6d 65 20 66 6f 72 0d 66 6f 72 |tle time for.for| 00000af0 65 67 72 6f 75 6e 64 20 61 63 74 69 76 69 74 69 |eground activiti| 00000b00 65 73 2e 20 54 72 79 20 74 68 69 73 20 2d 20 74 |es. Try this - t| 00000b10 77 6f 20 74 68 69 6e 67 73 20 6f 66 20 70 61 72 |wo things of par| 00000b20 74 69 63 75 6c 61 72 20 61 6d 75 73 65 6d 65 6e |ticular amusemen| 00000b30 74 20 61 72 65 0d 63 68 61 6e 67 69 6e 67 20 74 |t are.changing t| 00000b40 6f 20 4d 4f 44 45 30 20 61 6e 64 20 74 79 70 69 |o MODE0 and typi| 00000b50 6e 67 20 43 4f 4c 4f 55 52 20 32 39 20 74 68 65 |ng COLOUR 29 the| 00000b60 6e 20 43 4c 53 2e 20 59 6f 75 20 63 61 6e 20 77 |n CLS. You can w| 00000b70 61 74 63 68 20 65 78 61 63 74 6c 79 20 68 6f 77 |atch exactly how| 00000b80 0d 68 65 20 4f 53 20 73 65 74 73 20 61 6c 6c 20 |.he OS sets all | 00000b90 74 68 65 20 32 30 6b 20 6f 66 20 6c 6f 63 61 74 |the 20k of locat| 00000ba0 69 6f 6e 73 20 74 6f 20 32 35 35 2e 20 41 6c 73 |ions to 255. Als| 00000bb0 6f 2c 20 69 66 20 79 6f 75 20 68 61 76 65 20 69 |o, if you have i| 00000bc0 74 2c 20 70 6c 61 79 0d 48 6f 70 70 65 72 20 61 |t, play.Hopper a| 00000bd0 74 20 6c 6f 77 20 73 70 65 65 64 20 2d 20 79 6f |t low speed - yo| 00000be0 75 20 63 61 6e 20 68 65 61 72 20 74 68 65 20 69 |u can hear the i| 00000bf0 6e 64 69 76 69 64 75 61 6c 20 6e 6f 74 65 73 20 |ndividual notes | 00000c00 69 6e 20 74 68 65 20 65 6e 76 65 6c 6f 70 65 73 |in the envelopes| 00000c10 0d 75 73 65 64 20 74 6f 20 63 72 65 61 74 65 20 |.used to create | 00000c20 74 68 65 20 74 75 6e 65 20 61 6e 64 20 73 6f 75 |the tune and sou| 00000c30 6e 64 20 65 66 66 65 63 74 73 2e 20 0d 0d 57 61 |nd effects. ..Wa| 00000c40 72 6e 69 6e 67 20 2d 20 64 6f 20 6e 6f 74 20 75 |rning - do not u| 00000c50 73 65 20 74 68 69 73 20 77 69 74 68 20 74 68 65 |se this with the| 00000c60 20 22 53 4e 41 50 49 54 22 20 52 4f 4d 20 74 68 | "SNAPIT" ROM th| 00000c70 61 74 20 49 20 73 65 6e 74 20 61 20 66 65 77 20 |at I sent a few | 00000c80 69 73 73 75 65 73 0d 62 61 63 6b 20 61 73 20 69 |issues.back as i| 00000c90 74 20 6d 6f 6e 69 74 6f 72 73 20 74 68 65 20 31 |t monitors the 1| 00000ca0 4d 48 7a 20 62 75 73 20 69 6e 74 65 72 72 75 70 |MHz bus interrup| 00000cb0 74 20 6c 69 6e 65 20 61 6e 64 20 73 74 61 72 74 |t line and start| 00000cc0 73 20 74 68 65 20 64 69 73 6b 20 64 72 69 76 65 |s the disk drive| 00000cd0 0d 75 70 20 65 76 65 72 79 20 74 69 6d 65 20 6e |.up every time n| 00000ce0 49 52 51 20 67 6f 65 73 20 6c 6f 77 21 20 49 66 |IRQ goes low! If| 00000cf0 20 79 6f 75 20 66 65 65 6c 20 74 68 65 20 6e 65 | you feel the ne| 00000d00 65 64 20 74 6f 20 70 72 65 73 73 20 42 52 45 41 |ed to press BREA| 00000d10 4b 20 77 69 74 68 20 74 68 65 0d 73 6c 6f 77 65 |K with the.slowe| 00000d20 72 20 64 6f 77 6e 65 72 20 70 6c 75 67 67 65 64 |r downer plugged| 00000d30 20 69 6e 20 74 68 65 6e 20 6d 61 6b 65 20 73 75 | in then make su| 00000d40 72 65 20 79 6f 75 20 74 75 72 6e 20 74 68 65 20 |re you turn the | 00000d50 70 6f 74 20 64 6f 77 6e 20 74 6f 20 7a 65 72 6f |pot down to zero| 00000d60 0d 72 65 73 69 73 74 61 6e 63 65 20 6f 74 68 65 |.resistance othe| 00000d70 72 77 69 73 65 20 20 61 6e 20 49 52 51 20 6f 63 |rwise an IRQ oc| 00000d80 63 75 72 73 20 64 75 72 69 6e 67 20 72 65 73 65 |curs during rese| 00000d90 74 2e 20 4e 61 73 74 79 21 20 6c 65 74 20 6d 65 |t. Nasty! let me| 00000da0 20 6b 6e 6f 77 20 68 6f 77 0d 79 6f 75 20 67 65 | know how.you ge| 00000db0 74 20 6f 6e 2e 2e 2e 0d 0b 20 20 20 20 20 20 20 |t on..... | 00000dc0 20 20 20 20 20 20 20 20 20 20 20 20 52 6f 62 65 | Robe| 00000dd0 72 74 20 53 70 72 6f 77 73 6f 6e 2e 20 20 0d 81 |rt Sprowson. ..| 00000de0 20 20 0d | .| 00000de3
F/+CIRC1.m0
F/+CIRC1.m1
F/+CIRC1.m2
F/+CIRC1.m4
F/+CIRC1.m5
.