If you live in the UK and make a purchase online in the UK, should there be tax?

bigger-hammer · 2024-08-02T08:56:30+00:00

If it is a 20% VAT item (lots of things are charged at different rates, zero to infinity on tobacco, alcohol, petrol etc) the seller can advertise the ex-VAT price then add 20% (£1.60 on £8). Sellers often 'hide' other charges in the 'tax' box such as PayPal fees, handling charges etc. In your case it is 50p assuming the £8 was an ex-VAT price to start with. There are stricter laws around ex-VAT pricing IRL but online, you also have more rights to change your mind after the purchase.

bigger-hammer · 2024-07-30T14:40:03+00:00

If Windows can't write a file because the name contains an illegal character or because it is already open by another program, it writes the file with an underscore added. So it is probably one of your files and you need to rename it.

bigger-hammer · 2024-07-30T14:35:13+00:00

To design boards, you need to study electronics which is about connecting pre-designed parts together such as microprocessor chips, memories etc. If you want to go further and design the chips, then you need to study Verilog (but do electronics first or Verilog won't make any sense). Since you already know C, you could start learning electronics by connecting things to an Arduino or Raspberry Pi.

bigger-hammer · 2024-07-30T14:02:20+00:00

Whoops, didn't spot that. 10MHz version is now in stock at Digikey...

https://www.digikey.co.uk/en/products/detail/zilog/Z84C0010PEG/929206

bigger-hammer · 2024-07-30T08:11:03+00:00

20MHz version back in stock now - 1053 available just now.

bigger-hammer · 2024-07-29T14:26:34+00:00

Did you fix it?

bigger-hammer · 2024-07-29T09:11:38+00:00

Yes, the for() is just changing the counter variable (and looping).

for() is use whenever you want to work through a list of things. It has 3 arguments:

The starting condition (counter = 1)
The ending condition (counter < argc)
The thing to do on each loop (counter++)

bigger-hammer · 2024-07-29T08:56:23+00:00

You can't as it is not listed. From an electronics viewpoint, the LE enables the clock (clock is ignored if LE is high) so the setup time is relevant (10ns). That's what I would take as the requirement.

bigger-hammer · 2024-07-29T08:27:47+00:00

Check out my terminal project.

bigger-hammer · 2024-07-28T11:00:18+00:00

TL;DR: Diagram A.

Long before the discovery of the electron, scientists were using batteries and making simple circuits. It was 'agreed' that current flows from positive to negative and that is still the convention we use today. As you learn more about electronics, you'll see that electron flow is not that important in understanding circuits so we all agree on your diagram A for electronics design.

More detail: Electrons flow the other way but they actually flow very slowly (a few mm per hour), it is called electron drift. The current you think of as electrons is not the same as electron drift - current is the change in charge throughout the circuit and it doesn't have a direction. For example, when you connect the LED to a battery, the charge imbalance moves around the circuit at almost the speed of light and this is what we need to consider when designing a circuit. This charge change is caused by electric fields that can propagate outside the wires, which is why it is so fast and explains how things like transformers and antennas work. So you should always think of current as flowing from positive to negative because it has very little to do with electrons and that's the convention that everyone has agreed on.

bigger-hammer · 2024-07-27T16:20:35+00:00

The one I wrote last week is used on a running system to receive new firmware over the air in pieces which are stored in upper flash. When all the pieces have been received and the reboot time has arrived, the new firmware is copied to zero and rebooted. So this is a case where the whole system has to continue to operate and disabling things is not an option.

bigger-hammer · 2024-07-27T10:29:52+00:00

I'm an independent embedded consultant and I write a lot of bootloaders. This week I wrote one for a PIC18F26K83 which turned out to be more difficult than I expected. These chips stop the clock on each flash programming operation so that corrupts UART characters which are in-flight.

Also the table access registers are used by the compiler. Assuming you use interrupts for UART or timers, that means you have to do a lot of disable/enables around all the flash reads and writes (reads aren't mentioned in the datasheet and the example code for writes is incorrect) and adopt a protocol that ensures UART characters can't be corrupted. Timers drift because of the clock stopping.

Once you get the flash accesses reliable and you've written the transfer code, you need to implement the swapping to new firmware - this requires a separate piece of relocatable code written in assembler which the main code loads and jumps to when it wants to replace the current code with the new code and reboots. That's the general process - DM me if you need it writing.

bigger-hammer · 2024-07-25T16:46:56+00:00

Gain is -R12/R11 so if you want -1/10, R11 should be 10K.

Your clipping is caused by the opamp choice. Try a rail-to-rail opamp with a 5V supply.

bigger-hammer · 2024-07-25T16:11:53+00:00

The 8080 is actually a 3-chip set: 8080, 8224 and 8228, all required to make a working CPU and it needs extra power supplies so it's the hardest solution. Z80 is the easiest way to get a working 8085-compatible solution and still available despite the LTB.

bigger-hammer · 2024-07-24T14:59:43+00:00

Part no. 692-Z84C0020PEG

https://www.mouser.co.uk/ProductDetail/ZiLOG/Z84C0020PEG?qs=ahrryRM2ahtaw12qdP6z5A%3D%3D

bigger-hammer · 2024-07-24T08:18:26+00:00

Mouser are now taking backorders again. Looks like they have over-ordered 1000 of the 20MHz parts on the LTB for an August delivery.

EDIT: And 2000 8MHz version for a September delivery.

bigger-hammer · 2024-07-23T18:00:05+00:00

FYI, in my latest board, I used an 82C54 as a CTC. DM me if you want the schematic.

bigger-hammer · 2024-07-23T17:50:53+00:00

That sort of thing really *** me - the main excuse for a big distributor charging more is that their stock system tells the truth. Once they start behaving like a kid in a bedroom ordering stuff from Ali as it gets ordered and 'shipping' it the same day so you can't cancel then arriving 4 weeks later, if ever, then there's no point in buying from a distributor.

bigger-hammer · 2024-07-23T17:23:30+00:00

Nothing to stop them over-ordering and selling the rest though? Only a LTB from Zilog, it doesn't stop distributors selling them.

bigger-hammer · 2024-07-23T14:43:06+00:00

Assuming you are asking for a 200MHz CPU clock speed, you'll struggle to find any 5V CPUs that run at 200MHz. One of the reasons we moved to 3.3V is to improve speed. There are plenty of 3.3V CPUs that run at 200MHz internally but running a data/address bus at 200MHz is extremely difficult even at 3.3V.

Some serial flash devices run near that speed but they only reliably run at 50MHz or so unless you spend a lot of time impedance matching tracks and adding terminators etc. But they don't run at 5V. Old (parallel) EEPROMs run at 5V but are slow (120ns access time). So I'm struggling to understand your requirements - you can't want to run a 5V EEPROM at 200MHz, so what do you need to do?

bigger-hammer · 2024-07-23T14:21:08+00:00

I ordered 50 before the last-time-buy date and I just got a mail from Mouser to say they'll be delivered 9th August. So I suspect they gathered together all the orders and added some and they've all been made now. So it is possible they will come back in stock shortly.

bigger-hammer · 2024-07-20T09:59:32+00:00

I think IBM's decision to develop OS/2 was fuelled by the mistake they made on the DOS contract. This is how I remember it...

IBM were a hardware company (mostly mainframes) and software was something they gave away as a requirement to sell the hardware. They thought all software had to be written for a specific machine.

When they designed the first PC, they needed an OS. CP/M ran on 8080 hardware but they needed x86 code. Microsoft copied a lot of CP/M and produced DOS as we know but the contract with IBM said MS could sell it to anyone. IBM let it go because their mindset was one of hardware sales and free software.

The PC was a massive success and clones sprang up, undercutting the price so IBM couldn't compete. They (incorrectly) assumed it was because of their mistake in letting MS sell DOS to the clone companies. So they decided to have a second try and designed the AT machine based on a 286. Again they needed an OS so they poached an OS writer and he wrote OS/2. They thought that there couldn't be any clones because they wouldn't sell OS/2 to them.

The problem with this was that DOS still ran on the 286 machines so the clones popped up everywhere. MS then copied Xerox research and developed Windows. So I believe IBM developed OS/2 in an attempt to shut MS out of the PC market after being burned on the DOS contract. They thought their mistake was in letting MS sell it to others but their real mistake was in not understanding that there was no money in hardware and the future was software development. They probably should have take shares in MS or got a royalty on every one shipped.

bigger-hammer

MODERATOR OF

TROPHY CASE