I am into a project where I need 2 establish communication between ADuc814(Master) and ADuc841(Slave). Master shud Receive data transmitted by Slave. I am unable to establish the comm. I feel there is no response 4rm slave as though master generates the clock and SS pin is low, slave does not response. Is it necessary that both master and slave should operate in same CLOCK?? For Hardware connection, MOSI, MISO, SCLK and SS pins of Master and Slave are connected. Foll is the code Master Code
#include <ADUC814.H> unsigned char Data[20]; //Store SPI Rx data in Memory void Uart_Tx(unsigned char AsciData); //Serial Tx sbit SS = 0xB5; void main() { char i; PLLCON = 0x00; //Core Clk = 16.6777MHz //////////baud 0f 4800//////// RCAP2H = -1; RCAP2L = 0x92; TH2 = -1; TL2 = 0x92; SCON = 0x50; T2CON = 0x34; ////////////////////////////// CFG814 = 0x01; // Enable P3.5,6,7 for SPI SPICON = 0x37; // Master, CPOH=1,CPOL=0 SS = 0; // Slave Select Enable for(i=0;i<20;i++) { SPIDAT = 0x00; // SPI Clock Generate while(!ISPI); ISPI = 0; Data[i] = (unsigned char)SPIDAT; } /////////Serial Tx SPI Data into UART////////// for(i=0;i<20;i++) { Uart_Tx(Data[i]); Uart_Tx('\n'); } ///////////////////////////////////////////// }
Slave Code, ADuC841
void main() { char i; SPICON = 0x24; // Slave, CPOH=1, CPOL=0 for(i=0;i<20;i++) { SPIDAT = 0x38; /*Transmit Dummy Data, Asci of '8' while(!ISPI); ISPI = 0; } }
Friendzzzz Please Help.........
SPI uses one master clock: derived from the master uC. There is no need to 'sync' the master & slave uC oscillators.
NOTE: Assuming that your slave is not radically below its minimum operational frequency, then the slave's internal state machine should be capable of shifting in the master's bits, using the master's clock signal.
You should identify what you have already done during your testing of the system...
Are you sure that the Master's MOSI is connected to Slave's MISO, etc? (double-check it).
Did you see the Master's clock on a scope? was it good?
Was the master's data also valid?
What did the slave's data look like?
Are your voltage levels okay? (Slave's thresholds consistent with Master's? --- I don't want to look up those device data-sheets just yet).
I have properly connected Masters MOSI, MISO, SS and SCLK to corresponding lines of Slave. I have also checked the clock on scope. The master (ADuC814) generates clock properly as per the program logic. Even SS pin is low throughout. Bt still no communication happens btween them. I changed the slave to ADuC814(earlier ADuC841), and made master transmit the data 2 slave and slave does UART o/p. This works absolutely fine. Here both master and slave operated at same core clock 16.67MHz.Then I changed the slave core clk to 8.3 MHZ, keeping master at 16.67MHz. This time some blanks appeared in between the output (I chkd on HyperTerminal). Don't know why?? Got 2 figure it out. But still I got some output on HT. However with ADuC841 as slave and slave is made to transmit the data to master(ADuC814), though I am able to see the SCLK that master generates, the MISO line of slave remains high always. Always blanks get printed on HT. This is what I am not able to get it?? The slave core clock is 11.0592Mz and master operates at 16.67MHz. Could there be some synchronization problem like rising edge of master and slave might be different due to different core clock??
There shouldn't be a problem that master and slave has different processor clocks. However, the slave normally has a limit on the SPI clock speed, i.e. that the processor clock (or device clock) must be n times higher than the SPI clock signal, to make sure that the SPI slave logic runs at enough speed to be able to react. Some processor may require that the SPI slave logic runs at 12 times the SPI clock but this number can vary from processor to processor.
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