Data Sheet

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25
ETHERIO24TCPDATASHEET
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SENDINGBYTESVIASPI
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TosendoutSPIdataonPortAthecommandthatneedstobesentout
requiresan"SA"prefixfollowedbythenumberofbytesyouwanttosend
followedbythedatastream.Tosendoutthefollowingbytes0xFF0xAA
0x55youwouldsendthefollowing"SA"+0x03+0xFF+0xAA+0x55
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RECEIVINGBYTESVIASPI
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ReceivingbytesviaSPIhappenswhenthebytesaresentout,forevery
bytethatisclockedout,thereisanincomingbytebeingreceived.The
numberofbytesreceivedisdeterminedbythenumberofbytesthathas
beensentout.
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InordertoreceivethenumberofbytesthatisexpectedfromtheSPI
device,Nullbyteswillhavetobesentout.SendingouttheNullbytesis
requiredtokeeptheSPIclockrunningsothatthereturndataisclocked
outfromtheSPIslavedevice.
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Therearenullbytessentintheexampleimagebelow,thiscanbeseenin
thelasttwobyteswhicharesent(implementedwithdon'tcares)andon
theinputpinyouwillhavethevaliddatafromthedevice.Thevaliddata
willbesentbackinthecommandresponsepacket.
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Note:youmayhavetosendoutleadingzero'sanddon'tcaresdependingon
deviceyouarecommunicatingwith.e.g.sevenleadingzero'sthena
startbitaspertheimagebelow.
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ExampleimageforSPIcommunicationswiththeMCP3004/3008using8bit
segmentstakenfromtheMCP3004./3008datasheet.
(http://www.microchip.com
)
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©
2013ElexolPtyLtd Revision1.3
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