Hardware Serial USB Cable

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BeanieBots

Moderator
Having the 5v available is a useful feature but couldn't see either the chipset used or if it supports the 'break' required for PICAXE downloads.
 
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westaust55

Moderator
Hi Ian,
Welcome to the PICAXE forum (obviously you have been a member for a while but this is your first post).

Have you tried one of these cables yourself. There are other non Rev Ed cables out their that give members of this forum grief for various reasons including hand shaking signals as BB has mentioned.

While the availability of +5V at the TTL end is a good idea, most PC's have a limited supply capability through a USB port (motherboard have fuses on them) and the cable is rated to deliver 50mA. enough to power a PICAXE alone for programming and maybe flash one LED but not to power some more extensive projects.

Another potential; area for problem is that if the cable output is truly TTL level, there is a differnece in voltage levels between TTL logic and CMOS logic that can cause problems. PIC and most other microcontrolelrs use CMOS technology so may need a TTL buffer or a Schmitt Trigger buffer between the cable and PIC chip.
 
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IanH1960

New Member
Hi,

Yes, I've visited the forum many times for information and guidance on many issues but have generally found what I have been looking for without having to post - a valuable resource. (The only answer I haven't found is when the 28X2 will be released! :))

I haven't tried the AVITResearch cable for programming the chip - I will try it when I get a chance.

I have however tried it for general data comms to the hardware serial pins and have it running successfully performing 2-way coms with a PC at 115200 baud. This worked at the first time of trying (once I got my TX and RX's the right way around) with a 28X1 and 16MHz resonator. This was on an existing application as a straight swap for an existing RS232/TTL converter module.

More details on this page for anyone interested -

http://buggies.builtforfun.co.uk/Sim/system_enhanced.php

I left the unit running for about 15 minutes without any apparent glitches - seemed to run consistently.

My interest in the cable was as an simpler alternative to MAX232 chip setups and just for data comms - the 5V supply current levels aren't enough for my purposes so I haven't tried to use that aspect of the functionality.

Ian
 
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inglewoodpete

Senior Member
Reading between the lines, I get the impression that the driver for this cable could be configured for both 'T' and 'N' polarities (to use PICAXE definitions). Ie optionally invert the polarity of the data. Are you able to confirm this?

As WA55 mentioned previously, does the driver allow the transmission of a 'hard break' signal? Most PICAXE forum members consider this to be a must. Talking to the hserial input without a MAX232 inverter is one thing but you don't want to purchase a second cable to program the PICAXE.

Peter
 
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IanH1960

New Member
I've now tried to download a program using the cable and the Program Editor appears unable to make contact with the chip.

There does not appear to be an option for inverting the polarity from T to N.

Ian
 
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jaka

Member
usb ports

WA55 Do all usb ports have fuse in them. If so, I have an old dell laptop that I bought SH.

The ports didn't work, but it came with a 2 port usb cardbus that works fine.

I have often thought about dismantling it just to have a look. It would appear to be a power problem as the leds on memory sticks don't come on.

Would it be easy to locate. Worse could it be a fuseable link that could look like a cap or resistance.

I would hate to take it apart, find nothing then struggle to get it back together.

JAKA.
 
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BeanieBots

Moderator
Most proabably fuseable resistors. They can look almost identical to ordinary resistors. With luck, you might have the type which are pure green with writing on. They are the same size and shape as a regular 1/2W resistor.
Others look like a cap. Often black and about the size of a 10nF ceramic.
 
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BeanieBots

Moderator
It shouldn't be too hard to trace the USB pin back to the first component which will be the "fuse". Check with an ohm-meter and then confirm against the writing if applicable. If you're not sure, post a picture.
 
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inglewoodpete

Senior Member
The specification for USB states that it should current limit rather than blow. A couple of years ago, I thought I'd blown the 5v supply to a USB port but it came back to life after a reboot. Phew!
 
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westaust55

Moderator
To my knowledge all motherbaords have a number of these fuses for the USB ports, keyboard etc.

As BB says, they are small and look like small resistors. Also ofen some distance away from the sockets so it is difficelt to tell what is a fuse and where it is without decent manuals. Older manuals did indicate the position but not these days in a throw-away world.

But find the blown one and repalce it and there is a good change your USB ports may again work.
 
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inglewoodpete

Senior Member
If they they are so small and unrecognisable, are they really replacable? Where would you get something that fitted or would you use a more conventional fuse and wires?

I don't have the problem right now but am interested to know what they look like. Can someone post a photo?
 
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slurp

Senior Member
We had an interesting event on the kids computer, there's a multi-card reader with USB in one of the drive slots. It's possible to insert a USB memory stick in the slot up-side-down, cheap housing I guess but it means that you short the connections - that kills this computer until you remove power.

It was an interesting time trying to solve the problem, when it seemed easily resolved, not repeatable until there was the additional info on it happening with this USB device! ;)

regards,
Colin
 
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Dippy

Moderator
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jaka

Member
Laptop USB

To those thinking of taking a laptop apart, don't. Took me 3 hrs to get nowhere. Then two days to put it back together again. Thanks BB for the tips on what to look for. In a nutshell, I chick'nd out before I even reached the vital area. Only three screws and two washers left over.
 
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papaof2

Senior Member
Like most devices, some laptops are easier to disassemble than others. I've replaced the keyboard on a Micron, the touchpad on a Compaq, and the backup battery on a couple of IBM ThinkPads.
On the other hand, I've been taking things apart for years - my mother told the story of me taking a toy electric train apart to see how it worked when I was 6 years old - and it still worked when I put it back together ;-)

John
 
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