Re: [Amforth] TWI - 7segment display Gravitech.us

[Jan K. <kro...@ho...>]

Dear Matthias,

Thanks for this. I have now a complete working I2C connection with my 7seg display and my arduino.
Now I working on the tmp75 temperature controller (i2c)
When this working I will publish the code for other newbies as I am!

Thanks to all they helped me in the last time, this is a great forum!!!

Cheers,


Jan kromhout
Sacharovlaan 3
3223HM Hellevoetsluis-NL

Op 3 jun. 2012 om 19:39 heeft Matthias Trute <mt...@we...> het volgende geschreven:

> Hi Jan,
> 
> I'm not an expert for TWI, some I've spend some time with EEPROM
> modules (dont use the code in the lib directory, its broken).
> 
>> Dear Erich, I have done what you wrote, seems to work.But when I look
>> to te code of twi.frt I see some strange thing, or missing
>> sommething. When I look into the code never is sending the address in
>> twi.start 
> 
> That is absolutly ok. The TWI/I2C bus has some unique characteristics,
> one is that it can be considered stateful. The master has to send a
> start condition (some special combinations of voltages of the affected
> lines) and only after successfully aquiring the bus the master can continue.
> 
> When the master has finished its job, it has to send a stop condition
> (some special voltage combination again) to release the bus for others
> (I2C is multi-master capable).
> 
> Usually the first thing a master has to do after getting the bus is to
> select a device to communicate with by sending one byte (In your
> case the 0x38). If the devices answers with an ACK (see TWI status),
> everything works fine and the next bytes may be transmitted.
> Things can get more complicated if the device has to send
> data back to the master (EEPROMs)...
> 
> Thus I suspect the arduino code sequence (I do not know the
> arduino language)
> 
> Wire.beginTransaction(_7SEG)
> ...
> Wire.endTransaction(_7SEG)
> 
> should be written as
> 
> 0x38 constant _7SEG
> twi.start    \ aquire bus
> _7SEG twi.tx \ select device
> ....
> twi.stop     \ release bus, maybe reset the device state as well
> 
> You may want to check the Atmel Appnote AVR315 for more information
> Its only 11 pages...
> 
> HTH
> Matthias
> 
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