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HCS12 SPI SS-line does not go low

Question asked by thommes on Feb 8, 2013
Latest reply on Feb 8, 2013 by Gordon S Doughman



I am interfacing an external Flash via SPI using a MC9S12D64 Controller. The SS-line has to be kept low, while reading data. So i did the following, to control the SS-Pin by myself. The Idea was:

1) pull SS low

2) SPI-Communication

3) bring SS back high


This is my Code:


void INIT_SPI()


DDRS |=11100000; //SS, MOSI, SCK as Outut

SPIBR = 0b00000000; // (0+1)*2^(0+1)=2

                             //=> 16MHz/2 = 8MHZ

SPICR1 = 0b01010000;

SPICR2 = 0b00000000; //SS not used by SPI

WOMS = 0;


After that i had expected, that when the command:

PTS = (PTS & ~0x80);

would set SS= 0 and

PTS = (PTS|0x80);

would set SS =1


but the SS-line stays high, whatever i do!


Has someone used the SPI-Interface in that way?


Using MOSI,MISO,SCK normal and manage the SS-line manually?

Perhaps someone has working Code, or can tell my where my mistake is?