LMH0318: Read / Write via 8-bit SPI PIC24E Inteface

Anthony Viale

Part Number: LMH0318

Hi,

I would like to use a LMH0318 with a PIC microcontroller (SPI controlled) but I am facing an issue when I read the datasheet. Currently I can't test the interface and code made to drive the chip.

Anyway, in the datasheet, in the SPI protocol part, it is said that Each SPI transaction to a single device is 17 bits long [...]. But the PIC only support 8-bit or 16-bit format (to send or receive). How am I supposed to do ? The only thing I can think of is to send 3 bytes (so 8-bit format) with :

- First byte contains R/W bit and ADDR[7:1] ;

- Second byte contains ADDR[0] and DATA[7:1]

-Third byte contains DATA[0] and dummy data (7 bits).

Is that so ? Will the LMH0318 discard the last 7 bits (dummy bits) ? Nothing is said in the datasheet (or I missed it).

Thanks for your help !

over 8 years ago

0 Michael Lu (Santa Clara) over 8 years ago

TI__Mastermind 29655 points

Hi Anthony,

When using the SPI interface, the LMH0318 treats the incoming data like a large shift register. As such, you will need to add dummy bits and simply discard these unused bits if your interface only supports sending 8-bits at a time. This is a common approach that is used.

We recently released a training video detailing how to use the SPI interface with our SDI devices when the FPGA/ASIC operates in 8-bit format. Please reference the video here: LMH12XX SPI Access Description Training Video

Thanks,

Michael

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LMH0318: Read / Write via 8-bit SPI PIC24E Inteface