Search found 455 matches

by tcat
Thu Dec 07, 2017 12:55 pm
Forum: Hardware
Topic: The Mandatory Modifications
Replies: 6
Views: 805

Re: The Mandatory Modifications

Hi Cristian, We went through `Microdrive design' topic together :-). Being no expert, please find my observations. This is a summary of mandatory modifications. 1. Add resistor R104 (82 Ω) in TR1 collector circuit. It should be noted that this resistor is fitted in a non-standard way in the collecto...
by tcat
Tue Dec 05, 2017 5:14 pm
Forum: Hardware
Topic: White Screen, no Microdrives Activity
Replies: 7
Views: 777

Re: White Screen, no Microdrives Activity

To diagnose which chip(s) are affected sort out the memory chips (TMS4164) VSS and Q pins. Pine 16 and 14. On good memory chips this should produce another black line on the screen. When you short out a memory chip without the screen image changing that is one of the affected chips. The memory are ...
by tcat
Mon Dec 04, 2017 8:36 pm
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10244

Re: Microdrive Unit Design

c) The presence or absence of the foil screen appears to affect reliability in either slot #1 or #2 (i.e. reliability improved with a foil-screen in both positions.) NB - in my QLs, I've switched-out the linear 5V regulators for various designs of switched-regulator - these may well generate more n...
by tcat
Mon Dec 04, 2017 1:19 pm
Forum: Hardware
Topic: ULA ZX8301 - TV Picture Capabilities
Replies: 62
Views: 7452

Re: ULA ZX8301 - TV Picture Capabilities

3) 16 color mode. This can be done externally with some logic that has to extract a 10MHz clock from the available 15MHz, and use it to sample and process RGB. An extra control bit could also be implemented using external logic. Hi, Dealing with some wave shaping at the Microdrive design topic, als...
by tcat
Mon Dec 04, 2017 11:26 am
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10244

Re: Microdrive Unit Design

Hi Martyn, Thank you for a very nice summary, I could not have done it better. a cheaply built hardware design, still working within a wide ranges of tolerances after over 30 years. I like the above argument, MD technology is so simple and we can still read very old tapes, to be compared with data C...
by tcat
Mon Dec 04, 2017 8:31 am
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10244

Re: Microdrive Unit Design

Hi Charles, Martyn, The picture with encoding is perfect. Now I learnt about phase locking of the clock, the series of "0" zeros purpose. I was also surprised to see 4-bit overlap on DATA tracks, I only thought of byte interleave given some info in Service Manual. There still remains a mys...
by tcat
Thu Nov 30, 2017 7:45 am
Forum: Hardware
Topic: ULA ZX8301 - TV Picture Capabilities
Replies: 62
Views: 7452

Re: ULA ZX8301 - TV Picture Capabilities

Hi Nasta, This is a very thorough explanation, and excellent read, too. I have also wondered how 68008 does read and write 16, and 32 byte entities over 8-bit data bus. Also, you described how some pins can be freed by supplying simple external logic, e.g. transistor+diode. In standard QL design the...
by tcat
Sun Nov 26, 2017 9:47 am
Forum: Software & Programming
Topic: Mortville Manor re-released
Replies: 8
Views: 2581

Re: Mortville Manor re-released

Hi, A little investigation at `lankhor.net' revealed game origin. First release 1987 Also known as Le Manoir de Mortevielle Developed by Lankhor Published by Lankhor Distributed by (unknown) Platforms MS-DOS, Amiga, Atari ST, Amstrad CPC, Sinclair QL Engine Mortevielle Could QL version predate PC on...
by tcat
Sun Nov 26, 2017 9:09 am
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10244

Re: Microdrive Unit Design

Hi, To decode/encode DME stream in TTL logic, some flip-flops and a delayed feedback is needed, interestingly this scheme is protected by U.S. patents. Possibly because this scheme is still used in field devices, magnetic credit cards, RFID technology, etc. I wonder how Sinclair did it in ZX8302, as...
by tcat
Sat Nov 25, 2017 5:52 pm
Forum: Hardware
Topic: Microdrive Unit Design
Replies: 118
Views: 10244

Re: Microdrive Unit Design

Hi, Now giving it a second thought. There is also `Differential Manchester Encoding', also known as, Biphase Mark Code (BMC), Frequency Modulation (FM), or F2F (frequency/double frequency). Unlike with Manchester encoding, only the presence of a transition is important, not the polarity. Which helps...

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