Title: Poor Port Protectionb
Post by: phophollety on February 10, 2010, 11:36:24 pm
Post by: phophollety on February 10, 2010, 11:36:24 pm
Hi guys...
I'm very interested about buying and use the bus pirate, but before that, I was analyzing a bit the electrical schematic. Well, in my 3 years of electrical engineering experience, I learned one stuff "unprotected IOs gets burned - ALWAYS", soo I saw that there is no protection from the uC to the target connector, even 47R series resistor and a diode clamp, nothing!
Take a look about the bus pirate schematic.
There is no protection, working with development, is very very common to get the IOs in short-circuit, or to vdd, gnd or any unexpected situation.
This will damage the PIC easily.
I designed this interface before know the pirate bus (for my old company), the target protection hardware was designed for easy maintenance and to be resistent for the lab and to field..
Also, this hardware is compatible with 3v3 and 5v systems as you can change the pull-up voltage and pull-up individualy two lines (sda and scl ), diode clamp protection, high voltage reversed power and short circuit, about every thing that can happen in the development enviroment.
I realy would like to suggest this schematic as a hardware improvement for the bus pirate project, only few resistors, capacitors, two 74126 chips, and few fets transistors.
If you think is too much, take a look into the Renesas E8 debugger and the Microchip ICD2 debugger, they all uses this protection ( or part of ) and there are no problems with extras capacitantes or delays.
here, the schematic.
http://rapidshare.com/files/348875667/U ... e.pdf.html (http://rapidshare.com/files/348875667/USB_Interface.pdf.html)
Best regards!
I'm very interested about buying and use the bus pirate, but before that, I was analyzing a bit the electrical schematic. Well, in my 3 years of electrical engineering experience, I learned one stuff "unprotected IOs gets burned - ALWAYS", soo I saw that there is no protection from the uC to the target connector, even 47R series resistor and a diode clamp, nothing!
Take a look about the bus pirate schematic.
There is no protection, working with development, is very very common to get the IOs in short-circuit, or to vdd, gnd or any unexpected situation.
This will damage the PIC easily.
I designed this interface before know the pirate bus (for my old company), the target protection hardware was designed for easy maintenance and to be resistent for the lab and to field..
Also, this hardware is compatible with 3v3 and 5v systems as you can change the pull-up voltage and pull-up individualy two lines (sda and scl ), diode clamp protection, high voltage reversed power and short circuit, about every thing that can happen in the development enviroment.
I realy would like to suggest this schematic as a hardware improvement for the bus pirate project, only few resistors, capacitors, two 74126 chips, and few fets transistors.
If you think is too much, take a look into the Renesas E8 debugger and the Microchip ICD2 debugger, they all uses this protection ( or part of ) and there are no problems with extras capacitantes or delays.
here, the schematic.
http://rapidshare.com/files/348875667/U ... e.pdf.html (http://rapidshare.com/files/348875667/USB_Interface.pdf.html)
Best regards!
Title: Re: Poor Port Protectionb
Post by: phophollety on February 19, 2010, 11:35:13 pm
Post by: phophollety on February 19, 2010, 11:35:13 pm
Hey guys.. come on! I'm trying to improve the port protection? Does nobody care about burn easily your bus pirate board?
Title: Re: Poor Port Protectionb
Post by: Sjaak on February 20, 2010, 12:36:06 am
Post by: Sjaak on February 20, 2010, 12:36:06 am
I'm sorry but that link doesn't work (for me) but I see the size is 70kb so you can attach it to the post (the limit is 400kb)
I haven't much experience with microcontroller in the buspirate but my experience is that PICmicros can withstand more violence thenone can expect. I've put many times wrong voltages/inputs connected to outputss to a pic and it still works, all without buffers or series resistors. AFAIK the input are internally protected by diodes and can handle (relative) high currents. Also most protocols can be use a HiZ mode so it is safer. If you use the buspirate in low voltage enviroments (eg 5v and lower) not much harm is done.
just my two cents
I haven't much experience with microcontroller in the buspirate but my experience is that PICmicros can withstand more violence thenone can expect. I've put many times wrong voltages/inputs connected to outputss to a pic and it still works, all without buffers or series resistors. AFAIK the input are internally protected by diodes and can handle (relative) high currents. Also most protocols can be use a HiZ mode so it is safer. If you use the buspirate in low voltage enviroments (eg 5v and lower) not much harm is done.
just my two cents
Title: Re: Poor Port Protectionb
Post by: ian on February 20, 2010, 08:11:50 am
Post by: ian on February 20, 2010, 08:11:50 am
I'm sorry, I thought I posted a reply here earlier, but I must not have pressed post before surfing on to something else.
Sure, it would be fine to add pin protection to the Bus Pirate. PIC pins are really resilient though. There are thousands of Bus Pirates out there, and I haven't heard a single confirmed report of ESD or other related electrical damage from normal (ab)use. Sure, a few arrive DOA or with dead pins on arrival, but I don't know of any that have been damaged by something like a short. I use my (many) pirates in the lab for all kinds of stuff, they get some serious abuse during development, and none have broken. SparkFun shipped a batch of Bus Pirates with a 5volt regulator to the 3.3volt PIC, and they still worked.
So, sure, lets talk about some kind of simple protection, but I'm not really seeing a need for it in practical terms.
Sure, it would be fine to add pin protection to the Bus Pirate. PIC pins are really resilient though. There are thousands of Bus Pirates out there, and I haven't heard a single confirmed report of ESD or other related electrical damage from normal (ab)use. Sure, a few arrive DOA or with dead pins on arrival, but I don't know of any that have been damaged by something like a short. I use my (many) pirates in the lab for all kinds of stuff, they get some serious abuse during development, and none have broken. SparkFun shipped a batch of Bus Pirates with a 5volt regulator to the 3.3volt PIC, and they still worked.
So, sure, lets talk about some kind of simple protection, but I'm not really seeing a need for it in practical terms.
Title: Re: Poor Port Protectionb
Post by: phophollety on February 25, 2010, 11:49:43 am
Post by: phophollety on February 25, 2010, 11:49:43 am
Hi guys, sorry by the delay.
Only a 47R series resistor and a clamp diode would be enough, I think it is not necessary to se the 74126 buffer as most tools uses, not becauses it does not works, but because can get the project more expensive, I do not know the BOM cost... but what about only 4 resistors and 4 clamps diodes? This will protect against short-circuit and reverse voltage....
The resistors are really important, in the past I experienced many IIC Tools being burned becuse the did not have any series protection resistor, only diodes clamps..
Are you planning any hardware interaction for the nexts months?
Regards,
Renan
Only a 47R series resistor and a clamp diode would be enough, I think it is not necessary to se the 74126 buffer as most tools uses, not becauses it does not works, but because can get the project more expensive, I do not know the BOM cost... but what about only 4 resistors and 4 clamps diodes? This will protect against short-circuit and reverse voltage....
The resistors are really important, in the past I experienced many IIC Tools being burned becuse the did not have any series protection resistor, only diodes clamps..
Are you planning any hardware interaction for the nexts months?
Regards,
Renan