Problem with reading register of deo nano's accelerometer

Hello everyone,

I am using deo nano and am trying to read the register of its accelerometer via I2C.

I have used the same program to read a value from eeprom register and it works out well.

But using the same program, I cannot get acknowledge signal at the moment I sent the device address(accelerometer). I have checked my timing diagram and have generated a slower clock that pass with accelerometer. I also use signaltap2 to check out the value of my internal register.

Here is the syntax:

// ADXL clock= 400kHz or 2.5uS or 125 samples of 50mHz.

// ADXL address= 0x53/1010011 (alt address pin grounded)

module ADXL_Read(

clk_50, //clock 50Mhz//

key,

I2C_sclk,

I2C_sdat,

);

input clk_50;

input [1:0] key;

output I2C_sclk;

inout I2C_sdat;

wire reset_n;

reg GO;

reg sdi;

reg sclk;

reg [6:0] count; // Create slower clock with 128 samples of 50Mhz

reg [6:0] sd_counter;

reg [6:0] slave_add = 1010011; // DEFINE SLAVE ADDRESS

reg [7:0] register_add = 00110010; // DEFINE REGISTER ADDRESS

reg [7:0] data; //Data that is read

assign reset_n= key[0];

// 50MHz clock is too fast for the our devive(in this case eeprom),

// therefore slower clk need to be generated

always@(posedge clk_50) count <= count + 1;

// key[0] is to reset the whole operation

// key[1] is to give a start signal

always@(posedge count[6] or negedge reset_n)

begin

if (!reset_n)

GO <= 0;

else

if (!key[1])

GO <= 1;

end

always@ (posedge count[6] or negedge reset_n)

begin

if(!reset_n)

sd_counter <= 6'b0;

else

begin

if (!GO)

sd_counter <= 0;

else

if (sd_counter < 52) //sd_counter maximum

sd_counter <= sd_counter + 1;

end

end

always@ (posedge count[6] or negedge reset_n)

begin

if (!reset_n)

begin

sclk <= 1;

sdi <= 1;

end

else

case (sd_counter)

6'd0 : begin sdi<=1; sclk<=1;end

//START

6'd1 : sdi <= 0;

6'd2 : sclk <= 0;

//SLAVE ADDR+Write(Control Byte)

6'd3 : sdi <= slave_add[6];

6'd4 : sdi <= slave_add[5];

6'd5 : sdi <= slave_add[4];

6'd6 : sdi <= slave_add[3];

6'd7 : sdi <= slave_add[2];

6'd8 : sdi <= slave_add[1];

6'd9 : sdi <= slave_add[0];

6'd10 : sdi <= 0; //Write(0)

6'd11 : sdi <= 1'bz;//Slave ACK

//SUB ADDR(WORD ADDRESS)

6'd12 : sdi <= register_add[7];

6'd13 : sdi <= register_add[6];

6'd14 : sdi <= register_add[5];

6'd15 : sdi <= register_add[4];

6'd16 : sdi <= register_add[3];

6'd17 : sdi <= register_add[2];

6'd18 : sdi <= register_add[1];

6'd19 : sdi <= register_add[0];

6'd20 : sdi <= 1'bz;//Slave ACK

//START

6'd21 : begin sdi <= 1; sclk<=1; end

6'd22 : sdi <= 0;

//SLAVE ADDR+Read(CONTROL BYTE)

6'd23 : sdi <= slave_add[6];

6'd24 : sdi <= slave_add[5];

6'd25 : sdi <= slave_add[4];

6'd26 : sdi <= slave_add[3];

6'd27 : sdi <= slave_add[2];

6'd28 : sdi <= slave_add[1];

6'd29 : sdi <= slave_add[0];

6'd30 : sdi <= 1; //Read(1)

6'd31 : sdi <= 1'bz;//Slave ACK

//Data read(DATA)

//Data byte 1

6'd32 : data[7]= I2C_sdat;

6'd33 : data[6]= I2C_sdat;

6'd34 : data[5]= I2C_sdat;

6'd35 : data[4]= I2C_sdat;

6'd36 : data[3]= I2C_sdat;

6'd37 : data[2]= I2C_sdat;

6'd38 : data[1]= I2C_sdat;

6'd39 : data[0]= I2C_sdat;

6'd40 : sdi <= 1'b1;//Master ACK

//Data byte 2

6'd41 : data[7]= I2C_sdat;

6'd42 : data[6]= I2C_sdat;

6'd43 : data[5]= I2C_sdat;

6'd44 : data[4]= I2C_sdat;

6'd45 : data[3]= I2C_sdat;

6'd46 : data[2]= I2C_sdat;

6'd47 : data[1]= I2C_sdat;

6'd48 : data[0]= I2C_sdat;

//stop

6'd49 : begin sdi <= 1'b0; sclk <= 1'b1; end

6'd50 : sdi <= 1'b1;

endcase

end

assign I2C_sclk = (((sd_counter >= 4)&(sd_counter <= 20))|((sd_counter >=24)&(sd_counter <=50)))? ~count[6] : sclk;

assign I2C_sdat = sdi;

endmodule

Here are the pin planner assignment:

I2C_sclk : F2; I2C_sdat : F1 ; clk_50 : R8 ; key[1] : E1 ; key[0] : J15 ;

Here are the signaltap node(trigger cond): sd_counter(don't care), I2C_sclk(don't care), I2C_sdat(don't care), GO(Rising edge).

Signal configuration for signaltap2: clock(count[5]), sample depth(1k), storage qualifier(continuous), trigger(sequential, pretrigger position, 1)

Note: make the "bus display format" of node "sd_counter" to be "unsigned decimal" for the ease of viewing.

I realize the problem happen when sdat at 6'd3 until 6'd9. Although I assign slave_add to be 1010011, it appears at the signal tap to be 1011011

Why does it happen?

I realize it is too much to ask. Please someone help me find out the solution. I have stuck in this problem for the last 3 days and have yet no idea.

Thank you so much for helping me.