Keep in mind that conventional D-connectors existed before the idea was thought up of making IDC versions that could connect to IDC cable. Hence the numbering gets a bit confusing. Atari, Amiga, Acorn and some early PC mice are ‘bus’ mice. Two TTL digital lines are encoded with square waves for each...

I strongly recommend you do use a resistor to pull up undriven address line inputs. For CMOS chips, a value of between 4.7kΩ and 10kΩ is suitable. If an address line for a CMOS SRAM is allowed to float, it will pick up interface and static charge from other conductors or conductive bodies/objects. A...

Dave wrote:You could have a physical witch to connect /WR. If you tie it to 5V it can’t be written. A mechanical pull-up.

I would prefer a wizard, they tend to be more reliable and trustworthy

Mark

Some questions: ⋅ Am I reading that correctly with regard to SCART going into the two different modes? Some TVs (not many these days) have a user control to select which input system to use on the first (if more than one) or only SCART input. Most automatically switch input mode depending...

SCART (under a different name) is a product of the French. They passed a law requiring this type of connector to be fitted to all consumer TV/video equipment. It then became popular across Europe. But it has never been popular in the USA. As far as I am aware, nearly all TVs sold in the USA do not h...

The 6502 CPU used in the BBC Micro only uses the data-bus when the CPU clock is high. Hence if you isolate the address and data lines, the video system can use the time when the CPU clock is low to get screen data from the main RAM. Hence no slowdown. Note that this does not apply if you want your 6...

The original cases were vacuum formed. This is where a flat sheet of plastic is heated, then a vacuum pulls the plastic over a mould to form the shape. Any cut-outs that are required then need to be machined out. Injection moulded cases are described by Rick Dickinson in some detail on this page . B...

A member of the Sinclair ZX World forum is trying to get a run of brand new Sinclair ZX80 cases manufactured. He says this: I've been working hard recently in getting together different manufacturers in order to produce an EXACT copy of the Sinclair ZX80 case, either the original, or the later injec...

These keyboards may have some problems, but then, there are not many keyboards that are over 30 years old that don’t have at least some problems...

Mine (see here) still works okay. Although I don’t use this machine as my regular QL.

Mark

Some early AT keyboards had a switch to select XT mode. Of course that won’t help if all you have are PS/2 keyboards... If you search the ‘net you will find that there are three keyboard protocols for the five pin DIN system. It should also be possible to use a microcontroller to carry out a convers...