I am facing some embarrassing problems recently.
After some trouble-shooting, I found that: We have Board-A and Board-B. Board-A and Board-B communicate to each other with a UART TTL Level Communication. The communication cable is around 80cm long. During the communication, I got a lot of UART errors.
My mission is to build a more reliable communication between Board-A and Board-B; but not allowed to modify the hardware design and baud-rate.
To me, it is not wise to use a UART TTL Level Communication between two boards. However, I am being told that, it is very popular to us to use a UART TTL Level Communication between two boards.
I tried to find some articles/documentation to convince the involved people, that, they should not use a UART TTL Level Communication between two boards. But I can not find anything useful. What I could find is something like: The UART usually does not directly generate or receive the external signals used between different items of equipment.
My question is: Where can I find some convincing articles/documentation to convince the involved people? (This is to avoid the future problems.) If I am not allowed to modify the hardware design and baud-rate, what choices do I have to build a more reliable communication?
Unfortunately, there is a huge amount of misinformation about RS232 - including in "standard texts" that really should know better!
My original EIA books are currently deep down in storage.For a number of years, I have just made use of pdf versions of language standards, and datasheets/application notes/... for whatever components/modules I'm using. But the TIA-232 standards requires payment, and I normally avoid such standards unless I really do need them - in this case, RS-232 is obsolete.
The most important parameters here is capacitance and the slew-rate control of the driver. So datasheets for some drivers will give more explicit information, based on capacitance and cable length. Then you will be able to find references to 1 km or more depending on cable and baudrate.
But the important thing is that the actual standard was made for 15m/50 feet, which does give an indication that RS-232 itself is designed for longer distances than raw logic-level signals. This was the scope of the previous discussion.
Next thing is that even if you can manage very long cable length with suitable cable capacitance and baudrate, few people will still use RS-232 for really long lengths. If optical isn't an option, then most people would go for a differential solution - RS-422/RS-485 or similar.
Indeed.
In fact, RS232 is specifically designed for the interface between a "modem" (DCE) and a DTE - and it is the purpose of the modem to provide the long-distance link...
the solution to the OPs problem is not making major rework and adding 232 transceivers, the solution is to make the hardware drive of the TTL levels solid
Erik
Drifting yes.
But it whas the OP who did add that additional question. This time about "external" communication.
If the OP wants the thread to drift, then sure I'll play.
I believe that, my ex-hardware-partner in my previous company can make the hardware drive of the TTL levels solid. But I guess that, he will choose RS232 interface instead for many reasons. In the past, I do not need to worry about this kind of problems.
However, in my current company, I don't think "we" know what is solid and robust.
"in my current company, I don't think 'we' know what is solid and robust"
Clearly not!
So you really need to hire someone who does know - either as a permanent employee, or on a temporary/consultancy basis.
We are a OOXX level-n qualified company.
I believe that, most companies here in Taiwan are very interested in improving the Quality Assurance System / Business Flow / Work Flow / Process Management / Project Management ...... ...... ......
But most companies here in Taiwan are not very interested in improving employees technical ability.
Putting a leopard into a turtle's team, does not change the overall speed.
We already have a consultancy from nearby university, but most universities here in Taiwan do not know much about advanced technology, and the real skills that a engineer would need.
Maybe this is also a common worldwide issue.
www.developer.com/.../what-happened-to-software-engineering.html
Most of the agile methodologies focus mainly on the process management topics and don't discuss construction techniques in their teachings (the main exception is Kent Beck and Extreme Programming). I believe this due to the agile methodologies assuming you are already doing the technical practices!
Unfortunately, in my career as a consultant and an agile coach, I have seen all too often that those engineering practices are being left behind.
When having logic-level communication between boards, or maybe through a ribbon cable, you would normally (unless the distance is very short and you are in good control of emissions etc) use buffer chips.
They have much larger current-drive capability. Sometimes reduced by having EMI filters that slows downs the flanks of the signals. And they have schmitt-trigger inputs that makes sure they don't produce spurious noise if the input signal have a slow flank overlayed with a bit of noise.
I don't know about your distances, but if inside the same enclosure, then you normally do not go for RS-232 or similar. RS-232 is intended for external signals, i.e. basically short-distance (a couple of meters) of box-to-box communication. As covered earlier - with low baudrate and good cables you could even go quite long. But the intention is basically 1-15 meters.
With multiple boards in the same enclosure, you normally have some form of shielding from the box. If not, then you must consider cables with shielding to avoid radiating too much noise. But then - anyone who uses a box without shielding just have to have the skills to make a PCB that doesn't radiate noise. In reality, you design PCB with well-placed ground planes to keep down radiation even if intending to place PCB inside shielded box.
But this is not advanced technology - this is very basic electonics!
I believe that, my ex-hardware-partner in my previous company can make the hardware drive of the TTL levels solid if you can show the schematic (only what is connected to TX and RX pins in both ends) I'm sure someone will have a so;ltion.
HOWEVER that does not belong in a Keil forum and since you say "toolset none" I can't suggest one to use.
jeff thomson???
Is Erik playing around and using monikers again?
;)
Is Erik playing around and using monikers again? no, but Keil is.
Jeff is the one that here signs off on licences and, evidently when Jeff signed on at this computer Keil changed the name in the forum access.
thanx for seeing it, will be corrected
Check that Keil didn't reactivate mails for every new post to threads too - they tend to like to add that setting whenever they can.
Is Erik playing around and using monikers again? I never used a monniker, I, as opposed to many, do not hide behind monnikers, I am willing to stand behind what I say.
"If I am not allowed to modify the hardware design and baud-rate, what choices do I have to build a more reliable communication?"
Exactly what problems do you have?
The normal way to get more reliable communication is to add error-detection and error-recovery.
So, one step up is to add parity. Then you find odd numbers of bit errors in a character. This worls well for both stream and block-level transfers.
If you have block-level transfers, it's natural to add a checksum (which in this case should not be a normall additive sum, but something like crc16, crc32, adler-32 or similar) to improve the chance to detect a broken packet.
Of course, detection must be complemented with recovery, i.e. retransmission in case of transfer errors.
A stupid way to solve potential tranfer problems is to just send everything multiple times. This is acceptable unless having commands that risks being executed multiple times.
Anyway - much of the potential help depends on if you sends streams of data or blocks of data on that serial link. If it isn't block-based commands but instead stream transfers, you would normally instead reduce the number of data-carrying bits in each character sent, to let you use more bits for error detection and potentially error-correction. In short - by trying to get a higher hamming distance between the symbols.
In some cases, (such as when transmitting sound streams) you can improve the reliability by interleaving multiple sound samples over a couple of transmitted bytes. So if you get a "drop out", you only lost bandwidth of the transmitted signal - you recreate the lost data from bits transmitted before/after the drop. With ability to step up the bandwidth, you could recover without quality loss by having enough redundancy.
Interlaving without stepping up the bandwidth normally only works with sound, where you only affect the quality with transfer errors. If sending commands or text or similar, then you just have to have retransmission or redundant transfers to be able to get a 100% correct recovery (or know that the link transfer is bad beyond repair).