is this a toggle ?!

[Amit]

Hi group,

I'm working on project (basic) to learn VHDL and the purpose of
process (which had made so confused and mad). Anyway, I have question
and need to know how I can create a toggle flipflop using D f/f.

This is what that I think it should be but don't know how to get a
confirm so I will appreciate it if somebody could tell me if I'm on a
right track or no (the same as process);

What it must be is the output (q) which clocks another component and
qbar which goes back in d (input). Any comment?



LIBRARY ieee;
USE ieee.std_logic_1164.all;


ENTITY toggle IS

PORT(

d: IN STD_LOGIC;
rcClk: IN STD_LOGIC;
q: BUFFER STD_LOGIC;

qbar: OUT STD_LOGIC
);

END toggle ;


ARCHITECTURE beh OF toggle IS
BEGIN

PROCESS(rcClk)
BEGIN

IF (rcClk'EVENT AND rcClk = '1') THEN

q <= d;

END IF;

END PROCESS;

qbar <= NOT (q);

END beh;

 

[Amit]

Hi group,

I'm working on project (basic) to learn VHDL and the purpose of
process (which had made so confused and mad). Anyway, I have question
and need to know how I can create a toggle flipflop using D f/f.

This is what that I think it should be but don't know how to get a
confirm so I will appreciate it if somebody could tell me if I'm on a
right track or no (the same as process);

What it must be is the output (q) which clocks another component and
qbar which goes back in d (input). Any comment?

LIBRARY ieee;
USE ieee.std_logic_1164.all;

ENTITY toggle IS

PORT(

d: IN STD_LOGIC;
rcClk: IN STD_LOGIC;
q: BUFFER STD_LOGIC;

qbar: OUT STD_LOGIC
);

END toggle ;

ARCHITECTURE beh OF toggle IS
BEGIN

PROCESS(rcClk)
BEGIN

IF (rcClk'EVENT AND rcClk = '1') THEN

q <= d;

END IF;

END PROCESS;

qbar <= NOT (q);

END beh;

Ok, now I think this must the one. Would you please consider the
following code instead?
I have changed inteface modes



ENTITY toggle IS

PORT(

d: IN STD_LOGIC;
rcClk: IN STD_LOGIC;
q: BUFFER STD_LOGIC;


--qbar: OUT STD_LOGIC
qbar: BUFFER STD_LOGIC
);

END toggle;


ARCHITECTURE beh OF toggle IS
BEGIN

PROCESS(rcClk)
BEGIN

IF (rcClk'EVENT AND rcClk = '1') THEN

--q <= d;
q <= qbar;

END IF;

END PROCESS;

qbar <= NOT (q);

END beh;

 

[KJ]

<Snip>

You may want to consider putting a bit more thought into the question
that you'd like the group to answer before just posting code and
simply asking 'Any comments?'.

My comments
1. Your design works exactly as written.
2. Your design may not work as you intended (but without any
description from you it's not clear what your intended design should
be).
3. I'll bet signal 'q' has trouble getting out of the 'U' state.

KJ

 

[Amit]

<Snip>

You may want to consider putting a bit more thought into the question
that you'd like the group to answer before just posting code and
simply asking 'Any comments?'.

My comments
1. Your design works exactly as written.
2. Your design may not work as you intended (but without any
description from you it's not clear what your intended design should
be).
3. I'll bet signal 'q' has trouble getting out of the 'U' state.

KJ

Thanks I had no idea.

 

[Mike Treseler]

This is a good example of wires
getting in the way of a logical
description. I expect that the
operation you need could be
described as

if t = '1' then
toggle_v := not toggle_v;
end if;

The missing piece is a synchronous
template in which to insert this procedure.

I would do it as shown below.

-- Mike Treseler

__________________________________

library ieee;
use ieee.std_logic_1164.all;

entity toggle is
port (
clock : in std_ulogic;
reset : in std_ulogic;
t : in std_ulogic;
q : out std_ulogic
);

end entity toggle;

architecture synth of toggle is
begin
toggle : process(reset, clock) is
variable toggle_v : std_ulogic ;
------------------------------------------------------------------
-- Template Procedures: Always same three names. Contents varies.
------------------------------------------------------------------
procedure init_regs is -- init of register variables only
begin
toggle_v := '0';
end procedure init_regs;
------------------------------------------------------------------
procedure update_regs is -- distilled functional description
begin
if t = '1' then
toggle_v := not toggle_v;
end if;
end procedure update_regs;
------------------------------------------------------------------
procedure update_ports is -- wire register variables out to port
begin
q <= toggle_v;
end procedure update_ports;

------------------------------------------------------------------
-- Single Process Template -- Always exactly the same:
------------------------------------------------------------------
begin -- process template
if reset = '1' then
init_regs;
elsif rising_edge(clock) then
update_regs;
end if;
update_ports;
end process toggle;
end architecture synth;

 

[Amit]

This is a good example of wires
getting in the way of a logical
description. I expect that the
operation you need could be
described as

if t = '1' then
toggle_v := not toggle_v;
end if;

The missing piece is a synchronous
template in which to insert this procedure.

I would do it as shown below.

-- Mike Treseler

__________________________________

library ieee;
use ieee.std_logic_1164.all;

entity toggle is
port (
clock : in std_ulogic;
reset : in std_ulogic;
t : in std_ulogic;
q : out std_ulogic
);

end entity toggle;

architecture synth of toggle is
begin
toggle : process(reset, clock) is
variable toggle_v : std_ulogic ;
------------------------------------------------------------------
-- Template Procedures: Always same three names. Contents varies.
------------------------------------------------------------------
procedure init_regs is -- init of register variables only
begin
toggle_v := '0';
end procedure init_regs;
------------------------------------------------------------------
procedure update_regs is -- distilled functional description
begin
if t = '1' then
toggle_v := not toggle_v;
end if;
end procedure update_regs;
------------------------------------------------------------------
procedure update_ports is -- wire register variables out to port
begin
q <= toggle_v;
end procedure update_ports;

------------------------------------------------------------------
-- Single Process Template -- Always exactly the same:
------------------------------------------------------------------
begin -- process template
if reset = '1' then
init_regs;
elsif rising_edge(clock) then
update_regs;
end if;
update_ports;
end process toggle;
end architecture synth;

Mike THANK YOU so much. I have not read about procedure yet but this
will be a good start. However, it is possible to make it work without
PROCEDURE? what I was thinking about a toggling f/f was that only with
these input and outputs:

d (input) q(output)

clk qBar (output)

where q goes out and qbar gets into the d.

any advice?

Regards,
ak

 

[Mike Treseler]

any advice?

Hire a tutor or a consultant.

-- Mike Treseler

 

[KJ]

Thanks I had no idea.

That much is clear

Going back to the opening paragraphs of your original post....

I'm working on project (basic) to learn VHDL and the purpose of
process (which had made so confused and mad).

Since you're trying to learn VHDL, it won't help much if anyone here gives
you the answer but I suppose a little guidance can't hurt.

Anyway, I have question
and need to know how I can create a toggle flipflop using D f/f.

Fair enough...but first you have to have the entity/architecture code for a
D flip flop. I'm not saying it's difficult to create but you do need to
have it to do your assignment and the first thing you'll need to do is
decide on the interface to that entity. Your basic run of the mill D flip
flop has only 'Clock' and 'D' as inputs and 'Q' as an output, that's it.
Fancier ones may have a 'Qbar' output and a 'Reset' input but they don't
have to. Anyway, decide on the interface you want for your D flip flop and
then code up the entity and then the architecture. Debug it to make sure it
is correct.

Now that the D flip flop is done, you have to USE it to create a toggle flip
flop. Using something does not mean changing it, it means to create an
instance of it and connect it up appropriately for you usage. What this
means is that when you finally get to the architecture code for the toggle
flip flop you will
- Instantiate the previously created D flip flop. (Ex: My_Dff : entity
work.D_FF port map(.....);
- Do not change ANY of the code for the D flip flop itself...you've debugged
it, it's working, leave it alone.

But first you again need to decide on what the interface is to your toggle
flip flop. Your basic run of the mill toggle flip flop has 'T', 'Clock' and
'Reset' inputs and a 'Q' output (again fancier ones may have 'Qbar' if you
feel it is appropriate). You'll notice that I list 'Reset' as one of the
'must have' inputs but I'll leave it to you to work out why a toggle flip
flop should always have a reset but a D flip flop does not.

Just like before with the D flip flop, work out what you want the interface
to be to your toggle flip flop and now you'll have the entity code for your
toggle flip flop. To do the architecture of the toggle flip flop, first
instanitate the D flip flop using the example above (since that is part of
the assignment). Now work out the logic you need to connect the input and
outputs appropriately.

The assignment is (I'm guessing) supposed to get you to think about
hierarchical design, breaking down a 'big' problem into a number of 'small'
problems, tying them together appropriately with wires and additional logic
if necessary. In this case, you've been told the hierarchy (toggle flip
flop made out of a D flip flop), you may also have been told the interfaces
(i.e. the VHDL entity) and it's up to you to work out the details in the
architecture body.

This is what that I think it should be but don't know how to get a
confirm so I will appreciate it if somebody could tell me if I'm on a
right track or no (the same as process);

You don't need people in a newsgroup to confirm that you're on the right
track. You simply need to read the assignment definition and then test your
design with a simulator.

Good luck on your studies

KJ

 

[Dave Pollum]

Mike THANK YOU so much. I have not read about procedure yet but this
will be a good start. However, it is possible to make it work without
PROCEDURE? what I was thinking about a toggling f/f was that only with
these input and outputs:

d (input) q(output)

clk qBar (output)

where q goes out and qbar gets into the d.

any advice?

Regards,
ak

Amit;
I highly recommend the book "Essential VHDL: RTL Synthesis Done Right"
as a good beginner's book. From the book's back cover: "Essential
VHDL starts with simple examples and slowly builds to cover the most
comples topics. It's great for the VHDL novice..."
HTH
-Dave Pollum