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Diffstat (limited to 'part_3/ex13/spi2dac.v')
| -rw-r--r-- | part_3/ex13/spi2dac.v | 128 |
1 files changed, 128 insertions, 0 deletions
diff --git a/part_3/ex13/spi2dac.v b/part_3/ex13/spi2dac.v new file mode 100644 index 0000000..586a231 --- /dev/null +++ b/part_3/ex13/spi2dac.v @@ -0,0 +1,128 @@ +//------------------------------
+// Module name: spi2dac
+// Function: SPI interface for MPC4911 DAC
+// Creator: Peter Cheung
+// Version: 2.0
+// Date: 8 Nov 2016
+//------------------------------
+
+module spi2dac (sysclk, data_in, load, dac_sdi, dac_cs, dac_sck, dac_ld);
+
+ input sysclk; // 50MHz system clock of DE1
+ input [9:0] data_in; // input data to DAC
+ input load; // Pulse to load data to dac
+ output dac_sdi; // SPI serial data out
+ output dac_cs; // chip select - low when sending data to dac
+ output dac_sck; // SPI clock, 16 cycles at half sysclk freq
+ output dac_ld;
+
+//-------------Input Ports-----------------------------
+// All the input ports should be wires
+ wire sysclk, load;
+ wire [9:0] data_in;
+
+//-------------Output Ports-----------------------------
+// Output port can be a storage element (reg) or a wire
+ reg dac_cs, dac_ld;
+ wire dac_sck, dac_sdi;
+
+ parameter BUF=1'b1; // 0:no buffer, 1:Vref buffered
+ parameter GA_N=1'b1; // 0:gain = 2x, 1:gain = 1x
+ parameter SHDN_N=1'b1; // 0:power down, 1:dac active
+
+ wire [3:0] cmd = {1'b0,BUF,GA_N,SHDN_N}; // wire to VDD or GND
+
+ // --- internal 1MHz symmetical clock generator -----
+ reg clk_1MHz; // 1Mhz clock derived from 50MHz
+ reg [4:0] ctr; // internal counter
+
+ parameter TC = 5'd24; // Terminal count - change this for diff clk freq
+ initial begin
+ clk_1MHz = 0; // don't need to reset - don't care if it is 1 or 0 to start
+ ctr = 5'b0; // ... Initialise when FPGA is configured
+ end
+
+ always @ (posedge sysclk)
+ if (ctr==0) begin
+ ctr <= TC;
+ clk_1MHz <= ~clk_1MHz; // toggle the output clock for squarewave
+ end
+ else
+ ctr <= ctr - 1'b1;
+ // ---- end internal 1MHz symmetical clock generator ----------
+
+ // ---- FSM to detect rising edge of load and falling edge of dac_cs
+ // .... sr_state set on posedge of load
+ // .... sr_state reset when dac_cs goes high at the end of DAC output cycle
+ reg [1:0] sr_state;
+ parameter IDLE = 2'b00,WAIT_CSB_FALL = 2'b01, WAIT_CSB_HIGH = 2'b10;
+ reg dac_start; // set if a DAC write is detected
+
+ initial begin
+ sr_state = IDLE;
+ dac_start = 1'b0; // set while sending data to DAC
+ end
+
+ always @ (posedge sysclk) // state transition
+ case (sr_state)
+ IDLE: if (load==1'b1) sr_state <= WAIT_CSB_FALL;
+ WAIT_CSB_FALL: if (dac_cs==1'b0) sr_state <= WAIT_CSB_HIGH;
+ WAIT_CSB_HIGH: if (dac_cs==1'b1) sr_state <= IDLE;
+ default: sr_state <= IDLE;
+ endcase
+
+ always @ (*)
+ case (sr_state)
+ IDLE: dac_start = 1'b0;
+ WAIT_CSB_FALL: dac_start = 1'b1;
+ WAIT_CSB_HIGH: dac_start = 1'b0;
+ default: dac_start = 1'b0;
+ endcase
+
+ //------- End circuit to detect start and end of conversion state machine
+
+ //------- spi controller FSM
+ // .... with 17 states (idle, and S1-S16
+ // .... for the 16 cycles each sending 1-bit to dac)
+ reg [4:0] state;
+
+ initial begin
+ state = 5'b0; dac_ld = 1'b0; dac_cs = 1'b1;
+ end
+
+ always @(posedge clk_1MHz) // FSM state transition
+ case (state)
+ 5'd0: if (dac_start == 1'b1) // waiting to start
+ state <= state + 1'b1;
+ else
+ state <= 5'b0;
+ 5'd17: state <= 5'd0; // go back to idle state
+ default: state <= state + 1'b1; // default go to next state
+ endcase
+
+ always @ (*) begin // FSM output
+ dac_cs = 1'b0; dac_ld = 1'b1;
+ case (state)
+ 5'd0: dac_cs = 1'b1;
+ 5'd17: begin dac_cs = 1'b1; dac_ld = 1'b0; end
+ default: begin dac_cs = 1'b0; dac_ld = 1'b1; end
+ endcase
+ end //always
+ // --------- END of spi controller FSM
+
+ // shift register for output data
+ reg [15:0] shift_reg;
+ initial begin
+ shift_reg = 16'b0;
+ end
+
+ always @(posedge clk_1MHz)
+ if((dac_start==1'b1)&&(dac_cs==1'b1)) // parallel load data to shift reg
+ shift_reg <= {cmd,data_in,2'b00};
+ else // .. else start shifting
+ shift_reg <= {shift_reg[14:0],1'b0};
+
+ // Assign outputs to drive SPI interface to DAC
+ assign dac_sck = !clk_1MHz&!dac_cs;
+ assign dac_sdi = shift_reg[15];
+endmodule
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