diff --git a/ch4/motorcontrol.sv b/ch4/motorcontrol.sv
new file mode 100644
index 0000000..8e62e9f
--- /dev/null
+++ b/ch4/motorcontrol.sv
@@ -0,0 +1,43 @@
+module motorcontrol #(parameter N=21)
+   (input logic clk,
+    input logic rst,
+    input logic direction, 
+    input logic [N-1:0] count_in,
+    output logic pwm);
+
+	typedef enum logic[1:0] {reset, high, low} pwm_state;
+	pwm_state state, next_state;
+
+	always_ff @(posedge clk) 
+		if (rst)
+			state <= reset;
+		else 
+			state <= next_state;
+
+	always_comb
+	begin 
+		case (state)
+			reset:
+				begin
+					pwm = 0;
+					if (rst == 0)
+						next_state = high;
+				end 
+			high:
+				begin
+					pwm = 1;
+					if (direction == 0 && count_in >= 21'd100_000)
+						next_state = low;
+					else if ( direction == 1 && count_in >= 21'd200_000)
+						next_state = low;
+					else 
+						next_state = state;
+				end
+			low: 
+				begin
+					pwm = 0; 
+					next_state = state;
+				end 
+		endcase
+	end
+endmodule
diff --git a/ch4/motorcontrol_tb.sv b/ch4/motorcontrol_tb.sv
new file mode 100644
index 0000000..1f71d1e
--- /dev/null
+++ b/ch4/motorcontrol_tb.sv
@@ -0,0 +1,29 @@
+`timescale 1ns/1ps
+
+module motorcontrol_tb();
+
+   logic clk;
+   logic rst;
+   logic direction;
+   logic [20:0] count;
+   logic pwm;
+
+   timebase test1 (clk, rst, count);
+
+   motorcontrol test2 (clk, rst, direction, count, pwm);
+
+   always
+      #5 clk = ~clk;  // period 10ns (100 MHz)
+   initial
+      clk = 0;
+
+   initial begin
+                rst = 1; direction = 0;   
+     #10;       rst = 0; 
+     #19999990; rst = 1; direction = 1;
+     #10;       rst = 0;
+     #19999990; rst = 1;                              
+     #10;       rst = 0;
+   end
+
+endmodule
diff --git a/ch4/vish_stacktrace.vstf b/ch4/vish_stacktrace.vstf
new file mode 100644
index 0000000..ac0fb7e
--- /dev/null
+++ b/ch4/vish_stacktrace.vstf
@@ -0,0 +1,48 @@
+# Current time Thu Feb 13 11:59:20 2025
+# Program = vish
+# Id = "10.6g"
+# Version = "2019.08"
+# Date = "Aug  3 2019"
+# Platform = win64
+
+Exception c0000005 has occurred at address 50862f76. Traceback:
+# 0    0x50862f76: 'Tk_UpdatePointer + 0x7ad6'
+# 1    0x50864aa0: 'Tk_GetSelection + 0x160'
+# 2    0x507e71c9: 'TkClipInit + 0xac9'
+# 3    0x50976c03: 'TclNRRunCallbacks + 0x63'
+# 4    0xef010bfa: 'Itcl_EvalMemberCode + 0x3ba'
+# 5    0xef011dbb: 'Itcl_ExecMethod + 0x23b'
+# 6    0xef019879: 'Itcl_EvalArgs + 0x1c9'
+# 7    0xef014b51: 'Itcl_HandleInstance + 0x2c1'
+# 8    0x50976c03: 'TclNRRunCallbacks + 0x63'
+# 9    0xef010bfa: 'Itcl_EvalMemberCode + 0x3ba'
+# 10   0xef011dbb: 'Itcl_ExecMethod + 0x23b'
+# 11   0xef019879: 'Itcl_EvalArgs + 0x1c9'
+# 12   0xef014b51: 'Itcl_HandleInstance + 0x2c1'
+# 13   0x50976c03: 'TclNRRunCallbacks + 0x63'
+# 14   0x5097586c: 'TclCleanupCommand + 0x88c'
+# 15   0x50978d4f: 'Tcl_EvalEx + 0x1f'
+# 16   0x507b431a: 'Tk_BindEvent + 0x91a'
+# 17   0x507ebd41: 'TkBindEventProc + 0x291'
+# 18   0x507fc614: 'Tk_HandleEvent + 0x2f4'
+# 19   0x507b12d5: 'TkStringToKeysym + 0x2bd5'
+# 20   0x507b21a8: 'TkStringToKeysym + 0x3aa8'
+# 21   0x50976c03: 'TclNRRunCallbacks + 0x63'
+# 22   0x5097586c: 'TclCleanupCommand + 0x88c'
+# 23   0x50978d4f: 'Tcl_EvalEx + 0x1f'
+# 24   0x507b431a: 'Tk_BindEvent + 0x91a'
+# 25   0x507ebd41: 'TkBindEventProc + 0x291'
+# 26   0x507fc614: 'Tk_HandleEvent + 0x2f4'
+# 27   0x507fb2da: 'TkDeleteThreadExitHandler + 0x31a'
+# 28   0x50a1d41c: 'Tcl_ServiceEvent + 0x9c'
+# 29   0x50a1d0b4: 'Tcl_DoOneEvent + 0x124'
+# 30   0x507faee5: 'Tk_MainLoop + 0x25'
+# 31   0x5083d282: 'Tk_MainEx + 0x932'
+# 32   0x401d3a00: 'Mtirpc_Init + 0x223c0'
+# 33   0x401d60a8: 'Mtirpc_Init + 0x24a68'
+# 34   0x405f1a6f: 'Tclsqlite_Init + 0x1a5f'
+# 35   0x2708259d: 'BaseThreadInitThunk + 0x1d'
+# 36   0x2806af38: 'RtlUserThreadStart + 0x28'
+StackWalk failed 0
+# End of Stack Trace
+
diff --git a/entities/motorcontrol.sv b/entities/motorcontrol.sv
deleted file mode 100644
index 57e9c08..0000000
--- a/entities/motorcontrol.sv
+++ /dev/null
@@ -1,10 +0,0 @@
-module motorcontrol 
-   (input logic clk,
-    input logic reset,
-    input logic direction, 
-    input logic [?:0] count_in,
-    output logic pwm);
-
-
-
-endmodule