Re: Microdrive Unit Design
Posted: Sat Nov 18, 2017 11:39 am
I have 3 microdrive units with just a single key (instead of the normal 2) - does anyone want one of these units to experiment with and compare?
RIP Sir Clive Sinclair 1940 - 2021
https://qlforum.co.uk/
It could be interesting. Can you tell something about their condition and price please?RWAP wrote:I have 3 microdrive units with just a single key (instead of the normal 2) - does anyone want one of these units to experiment with and compare?
Condition - they have been stored in a box with other spare microdrive units for a few years - they are pulled from systems and untested.Cristian wrote:It could be interesting. Can you tell something about their condition and price please?RWAP wrote:I have 3 microdrive units with just a single key (instead of the normal 2) - does anyone want one of these units to experiment with and compare?
thanks
This asymmetry is caused by the fact, that in one direction a higher coercive force is needed that in the other, to overcome erased record which is a singular in the top left quadrant. `Bre' - remanent magnetism of erased record, `Hce' - its coercive force.DATA 1 and DATA 2 are used to drive current sources for track 1 and track
2. When DATA 1 is h i g h , for example, current is pul led in one
di rect ion through the head, when it is low current is p u l l e d in
the other direct ion. Wr i t i n g is done wi th an asymmetric write
current. Because the erase function is carried out wi th a d.c. f ield
it is necessary to write 'ha rde r ' in one direction than in the other
to overcome residual magnet ism. Resistors R4 and R5 on pins 11 and 7
of IC1 are chosen to al low this action. Should a di f ferent tape be
introduced or a di f ferent head type be fitted these resistors would
also need to be changed.
The decoding/encoding, albeit FM or ME, seems easy as you explained using XOR function. I like the picture you shown at wiki, copying it here for clarity.In the record mode the modulator in IC23 converts the ones and zeros in the data into FM (frequency modulation) where there is always a transition at the beginning of the bit cell. If the data is a one there is a transition at the beginning and in the middle of the bit cell, which means essentially that the frequency doubles if the data contains ones.
Which helps to eliminate noise on tape.Unlike with Manchester encoding, only the presence of a transition is important, not the polarity.