On 9/2/14, 10:59 AM, "c...@isbd.net" <c...@isbd.net> wrote:
>I am trying to get my BBB to talk to an SSD1803a based LCD >(specifically a Midas MCCOG42005A6W) and I'm failing miserably at the >moment. :-( > >I bought the MCCOG42005A6W because it's 3.3 volt and I2C bus so >thought it would be simple. > >I'm fairly certain I have the connections correct etc. but I can't get >the i2cdetect command to 'see' the MCCOG42005A6W. Presumably until it >can see the device I'm not going to get any further. > >However I'm not absolutely sure that the MCCOG42005A6W works in a way >that i2cdetect will understand, I'll try and explain. > >The MCCOG42005A6W only brings out the I2C interface from the >underlying SSD1803a, each 'command' to the SSD1803a comprises a >control byte (of which only two bits are significant) and an 8-bit >command (which is a superset of the HD4478OU command set). Thus the >SSD1803a (and in turn the MCCOG42005A6W) *always* needs 16-bits to be >sent to it before it will respond with anything useful. Hence any >detection program that tries sending an I2C address followed by an >8-bit 'command' will not get any sort of response, will this confuse >i2cdetect? > >I do have a 'scope but not a logic analyser, I can't detect anything >useful happening on the clock or data lines with the 'scope but that >may simply be because it happens for too short a period for me to see >anything. > >Can anyone suggest how I can progress this? First you should read up on how i2c works. What you are looking for is a ACK or a NACK which occurs at the end of each byte transmitted. The slave keeps SDA pulled low to slow down the communications, but after that, it should go high on the next clock to indicate an ACK. I believe that i2cdetect is looking for a ACK to confirm that a device exists. The first byte should be the address and if you don¹t have the correct address, you won¹t see an ACK. Regards, John > >-- >Chris Green >· > >-- >For more options, visit http://beagleboard.org/discuss >--- >You received this message because you are subscribed to the Google Groups >"BeagleBoard" group. >To unsubscribe from this group and stop receiving emails from it, send an >email to beagleboard+unsubscr...@googlegroups.com. >For more options, visit https://groups.google.com/d/optout. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
