SPI MOSI is idle high

lpcware — Wed, 15 Jun 2016 19:38:35 GMT

Content originally posted in LPCWare by emp on Fri Sep 05 06:32:02 MST 2014
Hello,

currently i am building a ws2812 driver using the spi interface of the LPC11C14 (later it should run on a LPC1113).

The user manual on page 234 says "In this configuration, during idle periods: ... The transmit MOSI/MISO pad is in high impedance.". In this configuration means CPOL 0, CPHA 1 in my case. However this sentence is used for every CPOL, CPHA combination.

My Scope shows, that the MOSI line is high in the idle state. I have added an external 10 KOhm Resistor between ground and MOSI (Pull-Down).

Is there something wrong in my initialisation or is this an undocumentent fault? The errata sheet does not mention the spi. A search in this forum and the internet revealed nothing

        //MOSI, No PULL-UP/DOWN, No Hystersis, No Open Drain
        LPC_IOCON->PIO2_3 = (0x02 << 0) | (0x00 << 3) | (0x00 << 5) | (0x00 << 10);
        //SSL1
        LPC_IOCON->PIO2_0 = (0x02 << 0) | (0x00 << 3) | (0x00 << 5) | (0x00 << 10);

        //Hardware init (SSP1)
        LPC_SYSCON->SYSAHBCLKCTRL |= (1 << 18); //Power

        LPC_SYSCON->SSP1CLKDIV = 1;

        LPC_SYSCON->PRESETCTRL &= ~(1 << 2);    // Reset
        LPC_SYSCON->PRESETCTRL |= (1 << 2);             //Reset end

        //16 Bit Transfer, SPI Mode, CPOL 0, CPHA 1, Serial Clock Rate
        LPC_SSP1->CR0 = (0x0F << 0) | (0x00 << 4) | (0x00 << 6) | (0x01 << 7) | ((SystemAHBFrequency / (5000000 -1)) << 8);
        // No Loopback mode, SPI Disable, Master
        LPC_SSP1->CR1 = (0x00 << 0) | (0x00 << 1) | (0x00 << 2);
        //Clockprescaler to minimal value
        LPC_SSP1->CPSR = 2;

        LPC_SSP1->CR1 |= (1 << 1); //enable spi

I do not need the SCK and MISO Pins. Even SSL is for debugging only.

Thanks emp

Re: SPI MOSI is idle high

lpcware — Wed, 15 Jun 2016 19:38:36 GMT

Content originally posted in LPCWare by emp on Fri Sep 05 12:30:17 MST 2014
Is this a highly active board.... Not that nobody answered on my post. Nobody answered on any post in this sub board.

By the way I found my problem. The IO Pin of my lpc was broken. I watched the graph at my scope again and saw, that the IO Pin did never return to ground. Always around 0.8 volts. Now I use a new controller and everything works fine.

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SPI MOSI is idle high

Re: SPI MOSI is idle high