faiyaz
Newbie level 3
Dear All,
I am developing a hardware which has an MCU - AT91SAM7SE256 from Atmel. There are 6 Si3215(ProSLIC) devices and 2 Si3050(DAA) devices (both from SiLabs) interfaced to SPI master of this MCU in normal individual chip select mode. The frequency of SPI I am using is 4 MHz. The slave devices are placed in 2 columns of 4 devices each. So the trace lengths are big and I haven't provided any signal termination but there is a powerplane running below along the paths of all traces.
Now, when I try to communicate to these slave devices, some of them work fine but 2-3 of these slave devices send Hex. FF data all the time. I thought this might be the loading issue so i used buffer 74HC125 to provide more driving current on SPI clock and MOSI signals. But still one of the slave devices was behaving same. But I can see there is a reduction in number of Slaves having problem.
The datasheet of AT91SAM7SE says that it can provide maximum 8 mA current on its digital output pins and the datasheet of Si3215 or Si3050 say in their Absolute Maximum ratings that Max Input current on digital Input pins would be 10 mA. I am not sure what these values mean.
One interesting observation I have done is when i place the Oscilloscope probe on SPI clock signal, more number of slave devices on board start behaving(sending Hex. FF data) as described above. And it also happens sometime that when I remove the probe from SPI clock, the number of Slaves which were having problem originally, may get reduced.
Could this be a loading problem? or Could it be just an improper termination problem? Please explore you views and suggest your solutions.
Thanks in advance.
Faiyaz Pisuwala
I am developing a hardware which has an MCU - AT91SAM7SE256 from Atmel. There are 6 Si3215(ProSLIC) devices and 2 Si3050(DAA) devices (both from SiLabs) interfaced to SPI master of this MCU in normal individual chip select mode. The frequency of SPI I am using is 4 MHz. The slave devices are placed in 2 columns of 4 devices each. So the trace lengths are big and I haven't provided any signal termination but there is a powerplane running below along the paths of all traces.
Now, when I try to communicate to these slave devices, some of them work fine but 2-3 of these slave devices send Hex. FF data all the time. I thought this might be the loading issue so i used buffer 74HC125 to provide more driving current on SPI clock and MOSI signals. But still one of the slave devices was behaving same. But I can see there is a reduction in number of Slaves having problem.
The datasheet of AT91SAM7SE says that it can provide maximum 8 mA current on its digital output pins and the datasheet of Si3215 or Si3050 say in their Absolute Maximum ratings that Max Input current on digital Input pins would be 10 mA. I am not sure what these values mean.
One interesting observation I have done is when i place the Oscilloscope probe on SPI clock signal, more number of slave devices on board start behaving(sending Hex. FF data) as described above. And it also happens sometime that when I remove the probe from SPI clock, the number of Slaves which were having problem originally, may get reduced.
Could this be a loading problem? or Could it be just an improper termination problem? Please explore you views and suggest your solutions.
Thanks in advance.
Faiyaz Pisuwala
