Could you explain "BUT NOT signal_declaration" in this tutor

[fl]

Hi,

I learn concurrent clause from this link:

http://www.csee.umbc.edu/portal/help/VHDL/concurrent.html

I do not understand "BUT NOT signal_declaration", see below please.
Could you explain what it intends to say?

Thanks,




process_declarative_items are any of:
subprogram declaration
subprogram body
type declaration
subtype declaration
constant, object declaration
variable, object declaration
file, object declaration
alias declaration
attribute declaration
attribute specification
use clause
group template declaration
group declaration

BUT NOT signal_declaration, all signals must be declared outside the process.
sig1 <= sig2 and sig3; -- considered here as a sequential statement
-- sig1 is set outside the process upon exit or wait

 

[Jim Lewis]

It simply notes that signal declarations are not allowed in a process. Instead for most applications you declare them in the architecture.

From the perspective of a process with a sensitivity list that is intended to create combinatorial logic, this makes sense. However, from the perspective of a process with a wait statement (used frequently in testbenches), perhaps not.

 

[fl]

On Wednesday, July 30, 2014 3:42:26 PM UTC-4, Brian Drummond wrote:

On Wed, 30 Jul 2014 10:47:44 -0700, fl wrote:
I do not understand "BUT NOT signal_declaration", see below please.
Could you explain what it intends to say?

Simply put, signals are the means of communicating between processes. So
declaring a signal within a process, visible only within that process,
doesn't make a lot of sense.

- Brian

Thanks. I am clear about the signal declaration.
For "BUT NOT", it is a typo for "BUT NOTE"? Or something else?

 

[Brian Drummond]

On Wed, 30 Jul 2014 10:47:44 -0700, fl wrote:

Hi,

I learn concurrent clause from this link:

http://www.csee.umbc.edu/portal/help/VHDL/concurrent.html

I do not understand "BUT NOT signal_declaration", see below please.
Could you explain what it intends to say?

Simply put, signals are the means of communicating between processes. So
declaring a signal within a process, visible only within that process,
doesn't make a lot of sense.

- Brian

 

[rickman]

On 7/30/2014 4:23 PM, fl wrote:

On Wednesday, July 30, 2014 3:42:26 PM UTC-4, Brian Drummond wrote:
On Wed, 30 Jul 2014 10:47:44 -0700, fl wrote:
I do not understand "BUT NOT signal_declaration", see below please.
Could you explain what it intends to say?

Simply put, signals are the means of communicating between processes. So
declaring a signal within a process, visible only within that process,
doesn't make a lot of sense.

- Brian

Thanks. I am clear about the signal declaration.
For "BUT NOT", it is a typo for "BUT NOTE"? Or something else?

It is just English, not part of the formal language for VHDL.
process_declarative_items may be any of this list, but not a
signal_declaration.

--

Rick