1. Data Stack and Return Stack
T1: Combinational Logic Circuits
Data Stack and Return Stack
Lab 6
R. E. Haskell
© 2001 Richard E. Haskell and Darrin M. Hanna

2. A 32 x 16 Stack

3. A 32 x 16 Stack Module

4. stack_ctrl32 wr_addr rd_addr 00000 11111 entity stack_ctrl is port (
clr: in STD_LOGIC;
clk: in STD_LOGIC;
push: in STD_LOGIC;
pop: in STD_LOGIC;
we: out STD_LOGIC;
amsel: out STD_LOGIC;
wr_addr: out STD_LOGIC_VECTOR (4 downto 0);
rd_addr: out STD_LOGIC_VECTOR (4 downto 0);
full: out STD_LOGIC;
empty: out STD_LOGIC );
end stack_ctrl;
00000
wr_addr
rd_addr
11111

5. stack_ctrl32 architecture stack_ctrl_arch of stack_ctrl is
architecture stack_ctrl_arch of stack_ctrl is
signal full_flag, empty_flag: STD_LOGIC;
begin
stk: process(clr, clk, push, pop, full_flag, empty_flag)
variable push_addr, pop_addr: STD_LOGIC_VECTOR(3 downto 0);
if clr = '1' then
push_addr := "1111";
pop_addr := "0000";
empty_flag <= '1';
full_flag <= '0';
wr_addr <= "1111";
rd_addr <= "0000";
full <= full_flag;
empty <= empty_flag;

6. stack_ctrl32 wr_addr rd_addr 00000 elsif clk'event and clk = '1' then
11111
rd_addr
wr_addr
elsif clk'event and clk = '1' then
if push = '1' then
if pop = ‘0' then
if full_flag = '0' then
push_addr := push_addr - 1;
pop_addr := push_addr + 1;
empty_flag <= '0';
if push_addr = "11111” then
full_flag <= '1';
push_addr := "00000";
end if;
else
–- write to top of stack (pop_addr) without pushing
-- don’t change push_addr and pop_addr

7. stack_ctrl32 wr_addr rd_addr elsif pop = '1' then 00000
if empty_flag = '0' then
pop_addr := pop_addr + 1;
if full_flag = '0' then
push_addr := push_addr + 1;
end if;
full_flag <= '0';
if pop_addr = "00000" then
empty_flag <= '1';
wr_addr <= push_addr;
rd_addr <= pop_addr;
00000
11111
rd_addr
wr_addr

8. stack_ctrl wr_addr rd_addr 00000 full <= full_flag;
11111
rd_addr
wr_addr
full <= full_flag;
empty <= empty_flag;
if push = '1' and full_flag = '0' then
we <= '1';
else
we <= '0';
end if;
if push = '1' and pop = ‘1' then
amsel <= '1';
amsel <= '0';
end process stk;
end stack_ctrl_arch;

9. A 32 x 16 Stack Module

10. Data Stack

11. Return Stack