`timescale 1ns/1ps
`define DATAWIDTH 32
`define ADDRWIDTH 8
`define IDLE 2'b00
`define W_ENABLE 2'b01
`define R_ENABLE 2'b10
module APB_Slave
(
input PCLK,
input PRESETn,
input [`ADDRWIDTH-1:0] PADDR,
input PWRITE,
input PSEL,
input [`DATAWIDTH-1:0] PWDATA,
output reg [`DATAWIDTH-1:0] PRDATA,
);
reg [`DATAWIDTH-1:0] RAM [0:2**`ADDRWIDTH -1];
reg [1:0] State;
always @(negedge PRESETn or posedge PCLK) begin
if (PRESETn == 0) begin
State <= `IDLE;
PRDATA <= 0;
end
else begin
case (State)
`IDLE : begin
PRDATA <= 0;
if (PSEL) begin
if (PWRITE) begin
State <= `W_ENABLE;
end
else begin
State <= `R_ENABLE;
end
end
end
`W_ENABLE : begin
if (PSEL && PWRITE) begin
RAM[PADDR] <= PWDATA;
end
State <= `IDLE;
end
`R_ENABLE : begin
if (PSEL && !PWRITE) begin
PRDATA <= RAM[PADDR];
end
State <= `IDLE;
end
default: begin
State <= `IDLE;
end
endcase
end
end
endmodule
