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by tcat
Mon Nov 20, 2017 12:56 pm
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 95
Views: 5956

Re: Microdrive Unit Design

Hi Martin, This is excellent work, just studying the write waves for DATA1-2. I see some asymmetry here in shapes, I wish to ask about first, as my next post will be about asymmetric bias for FM recording. Y-axis is in Volts, but there are two rasters for Channel 1 (0,419 .. 5,18V) and 2 (0,968 .. 4...
by tcat
Fri Nov 17, 2017 10:46 am
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 95
Views: 5956

Re: Microdrive Unit Design

I borrow this explanation from other MD related thread. There is a small hole on the bottom of the motor. Through it you can adjust preset potentiometer to change speed. The potentiometer increases speed when turned clockwise (as viewed from bottom of motor). The speed range was quite limited, so ad...
by tcat
Wed Nov 15, 2017 10:14 am
Forum: Hardware
Topic: Engineering mules....
Replies: 16
Views: 650

Re: Engineering mules....

QL User article does jump to the same initialisation code (which is just after the memory check). Yes, I think that is precisely what it does, but that is not enough for a full recovery. I wonder what else is needed, close all channels, save system vars, but how to restore them, other? EDIT, this w...
by tcat
Wed Nov 15, 2017 8:54 am
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 95
Views: 5956

Re: Microdrive Unit Design

Hi Cristian, I wish I could explain that, my argument was that tape speed is one of the sensitive factors having some influence on it. Please consider: 0.25 secs * 10^6 / 31760 ~ 8 sectors. 1/4 of a second then corresponds to 8 sectors on tape, where each sector is 512 byte long. 225 nominal +/- 8 s...
by tcat
Tue Nov 14, 2017 8:45 am
Forum: Hardware
Topic: Engineering mules....
Replies: 16
Views: 650

Re: Engineering mules....

Yes, it would be a nice exercise.
As for QL ROM development archetypes, I remember seeing some collected by Urs Koening at one of his sites, at least I think they may be the prototypes you look for.
Tom
by tcat
Tue Nov 14, 2017 8:19 am
Forum: Hardware
Topic: Engineering mules....
Replies: 16
Views: 650

Re: Engineering mules....

Hi, just wandering what is the line, ZX8302 uses to raise `mdv gap interrupt' to MC6800. IPL1? There was a code handling NMI-7 `warm reset' published in some magazine, I have corrected. http://qlforum.co.uk/viewtopic.php?f=3&t=1427&hilit=warm+reset It clears the screen, jumps to some init ve...
by tcat
Sun Nov 12, 2017 5:19 pm
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 95
Views: 5956

Re: Microdrive Unit Design

If the above correct then 44 um (microns) of tape must accommodate 8 bits, and that is 2*8 FM transitions, we already learnt. How could this be at all achieved? The answer lies in the head construction and tape quality capable of enough magnetic density. Searching web shows many head types, but pri...
by tcat
Sun Nov 12, 2017 4:41 pm
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 95
Views: 5956

Re: Microdrive Unit Design

Hi,

@ Dex, picture showing it nicely.
@ Prof, yes the idea of reading two h/w registers, each having one byte of data from either track. Reading is driven by ZX8302 triggering a gap interrupt for MC68000.

Tom
by tcat
Sun Nov 12, 2017 12:07 pm
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 95
Views: 5956

Re: Microdrive Unit Design

Yes, I see. But how the tracks are switched to make a single continuous stream? byte-stream.png The QL Service Manual gives this explanation. 7.3.2 Data is recorded on two tracks using a standard stereo cassette head arrangement and is written in bytes, one byte to one track and the next byte to the...
by tcat
Sun Nov 12, 2017 10:50 am
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 95
Views: 5956

Re: Microdrive Unit Design

Hi, Yes, that is right! We have two tracks here of a stereo head (one erase coil is common to both tracks). With a mono head (one track) we would have needed 2x5080mm length of tape, and 2x7.19 secs of loop time to achieve 225 sectors. I may be wrong, can you please help as to which calculations nee...

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