Atmel AT91SAM7S Manchester encoder/decoder

An internet search turned up nothing usefull and on the at91.com I only found this message on the sam7 forum:

Seems he got it to work a little more than I, but not completely.

Isn't that the cause of your problem. I am not familiar with this UART but I remember from my Z80SIO in HDLC days that when the TX Empty interrupt was not serviced (new byte delivered) the CRC generation was triggered and flags were transmitted.

So in your case, using the timeout interrupt of the transmitter could be the triggering the preamble when the next byte is loaded into the UART. My guess is that you should use the Transmitter Empty (or whatever name is used) to load a new character in the UART.

Meindert

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Mmm.... apparently, the preamble is generated for every character (it says so on page 305 of the datasheet), which means that you enable the preamble for the first character in your frame and you disable it (set the length to

Meindert

I'm using the receiver timeout interrupt to signal received messages. This one is triggered when there is no character received for N bit times (I used N=20).

Changing the pre-amble length to zero after the first character is sent means I would need te put the first char seperately in the THR and can not use the fire-and-forget PDC option. I now send messages by setting the PDC's transmit pointer and counter regs, the rest is automatic. I am also not sure how the machester wil respond to changing the pre-amble length when it is transmitting (The tx-empty interrupt comes as soon as the char is transferred to the shift register).

But all that is problems for later. The more urgent problem (to me) is that the UART does not even regognize it's own transmission when RXD is loopped back to TXD and that there are glitches on the TXD signal.

I'm already working on another solution. I now encode the data myself in such a way that the sequence of startbit, data and stopbits already has zero DC offset, so I don't need the manchester for that anymore. The message is started with a series of sync chars that do not have valid data coding (sort of a pre-amble). That way I don't have to mess with the manchester encoder and the glitches are gone.

I would like to ask if you tried to contact Atmel about this? I have had a couple of detailed questions about some of the peripherals and have not been getting good responses from Atmel support. One problem with my latest inquiry is that the person who knew the answer (I guess there was only one person in the whole company) was on vacation. Being in France they have a different culture from the US in regards to vacations. My understanding is that most of Europe gets some 4 or more weeks of vacation a year and not after working at a company for 20 years!

If your complaints about the transmitter sending those brief pulses are accurate, I would think this would be in the errata. I don't know that

and The eurozone economy grew at its fastest rate for six years in the three months to June and even outpaced the US.(ft.com)

Even the french economy grew, so it can't be that bad can it!

martin

In article , rickman writes

This is correct. It is usual to have 4/5 weeks vacation + national holidays as soon as you start. It can progress up to 6+ weeks over the years.

The Swedes tend to shut down for about 6 weeks in the summer anyway. But then they do have a couple of months of near total darkness. The Parisians always close down for 2 weeks in August (some say it's the heat others that it is too many tourists :-).

Interestingly the Europeans are about as productive as the US (some a bit more some a bit less) so personally I prefer the system with the longer holidays.