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#use spi, selecting baud mode and slave select logic

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vsmguy

Joined: 13 Jan 2007
Posts: 91

#use spi, selecting baud mode and slave select logic

Posted: Fri Apr 19, 2013 1:28 pm

A SPI slave I am using (a FRAM device) requires me to hold the SS line low for multiple bytes in the same transaction (the first byte in a transaction is the command byte followed by context dependent bytes)

I would like to use a SPI clock frequency of 1MHz. The master is a PIC16F877A @20Mhz HS. The hardware SPI peripheral is unavailable.

My current soft SPI code looks like this:

Code:

#define FRAMSD_PIN_SELECT PIN_D0
#use spi(STREAM=SPI2, MASTER, bits=8, mode=3, DI=PIN_D3, DO=PIN_D2, CLK=PIN_D1)

1. What value of 'BAUD' should I select so that the SPI clock frequency is 1MHz? 1000000?

2. Also, is there a way to have the following hold the SS line low for multiple bytes in the same transaction or do I have to handle the ENABLE pin myself manually?

Code:

#use spi(STREAM=SPI2, MASTER, bits=8, mode=3, ENABLE=FRAMSD_PIN_SELECT, ENABLE_ACTIVE=0, DI=PIN_D3, DO=PIN_D2, CLK=PIN_D1, BAUD=<1MHz>)

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