diff --git a/vhdl/env1_globals.vhd b/vhdl/env1_globals.vhd
index 91493e1d..c4ef0df5 100644
--- a/vhdl/env1_globals.vhd
+++ b/vhdl/env1_globals.vhd
@@ -11,11 +11,11 @@ package env1_globals is
 
 -- file name and file size (in lines) of the file that is converted to the ROM located at 0x0000
 constant ROM_FILE             : string    := "../monitor/monitor.rom";
-constant ROM_SIZE             : integer   := 2202;
+constant ROM_SIZE             : integer   := 2250;
 
 -- size of lower register bank: should be 256
 -- set to 16 during development for faster synthesis, routing, etc.
-constant SHADOW_REGFILE_SIZE  : integer   := 16;
+constant SHADOW_REGFILE_SIZE  : integer   := 256;
 
 -- size of the block RAM in 16bit words: should be 32768
 -- set to 256 during development for tracability during simulation
diff --git a/vhdl/qnice_cpu.vhd b/vhdl/qnice_cpu.vhd
index 598e38e1..e77506c1 100644
--- a/vhdl/qnice_cpu.vhd
+++ b/vhdl/qnice_cpu.vhd
@@ -126,18 +126,18 @@ signal cpu_state           : tCPU_States := cs_reset;
 signal cpu_state_next      : tCPU_States;
 
 -- CPU i/o signals
-signal ADDR_Bus            : std_logic_vector(15 downto 0);
+signal ADDR_Bus            : std_logic_vector(15 downto 0) := (others => '0');
 signal DATA_Dir_Ctrl       : std_logic := '0';
-signal DATA_To_Bus         : std_logic_vector(15 downto 0);
+signal DATA_To_Bus         : std_logic_vector(15 downto 0) := (others => '0');
 signal DATA_From_Bus       : std_logic_vector(15 downto 0) := (others => '0');
 
 -- register bank signals for accessing R0 .. R13
-signal reg_read_addr1      : std_logic_vector(3 downto 0) := "0000";
-signal reg_read_addr2      : std_logic_vector(3 downto 0) := "0000";
+signal reg_read_addr1      : std_logic_vector(3 downto 0) := (others => '0');
+signal reg_read_addr2      : std_logic_vector(3 downto 0) := (others => '0');
 signal reg_read_data1      : std_logic_vector(15 downto 0);
 signal reg_read_data2      : std_logic_vector(15 downto 0);   
-signal reg_write_addr      : std_logic_vector(3 downto 0) := "0000";
-signal reg_write_data      : std_logic_vector(15 downto 0);
+signal reg_write_addr      : std_logic_vector(3 downto 0) := (others => '0');
+signal reg_write_data      : std_logic_vector(15 downto 0) := (others => '0');
 signal reg_write_en        : std_logic := '0';   
 
 -- registers R13 (SP), R14 (SR) and R15 (PC) are directly modeled within the CPU
@@ -147,14 +147,14 @@ signal SR                  : std_logic_vector(15 downto 0) := x"0001"; -- status
 signal PC                  : std_logic_vector(15 downto 0) := x"0000"; -- program counter (R15)
 
 -- intstruction related internal CPU registers
-signal Instruction         : std_logic_vector(15 downto 0); -- current instruction word
+signal Instruction         : std_logic_vector(15 downto 0) := (others => '0'); -- current instruction word
 signal Opcode              : std_logic_vector(3 downto 0);  -- current opcode, equals bits 15 .. 12
 signal Src_RegNo           : std_logic_vector(3 downto 0);  -- current source register, equals bits 11 .. 8
 signal Src_Mode            : std_logic_vector(1 downto 0);  -- current source mode, equals bits 7 .. 6
-signal Src_Value           : std_logic_vector(15 downto 0); -- the value is coming from a register or from memory
+signal Src_Value           : std_logic_vector(15 downto 0) := (others => '0'); -- the value is coming from a register or from memory
 signal Dst_RegNo           : std_logic_vector(3 downto 0);  -- current destination register, equals bits 5 .. 2
 signal Dst_Mode            : std_logic_vector(1 downto 0);  -- current destination mode, equals bits 1 .. 0
-signal Dst_Value           : std_logic_vector(15 downto 0); -- the value is coming from a register or from memory
+signal Dst_Value           : std_logic_vector(15 downto 0) := (others => '0'); -- the value is coming from a register or from memory
 signal Bra_Mode            : std_logic_vector(1 downto 0);  -- branch mode (branch type)
 signal Bra_Neg             : std_logic;                     -- branch condition negated
 signal Bra_Condition       : std_logic_vector(2 downto 0);  -- flag number within lower 8 bits of SR