Disconnection specification

disconnect guarded_signal_specification after time _expression ;

• entity_declarative_part
• architecture_declarative_part
• package
• block_declarative_part

guarded _signal_list : type_mark

• relation { and relation }
• relation { or relation }
• relation { xor relation }
• relation [ nand relation ]
• relation [ nor relation ]
• relation { xnor relation }

a is declared as a guarded signal of the type REGISTER . If during simulation a driver for the signal a is deactivated this happens with a delay of 1ns.

SIGNAL a : resolved_type REGISTER ;
DISCONNECT a : resolved_type AFTER 1 ns;

sig1 , sig2 and sig3 are declared as guarded signals of the type REGISTER . During simulation the drivers for sig1 are switched off with a delay of 5 ns and those of the other signals with a delay of 8 ns.

SIGNAL sig1, sig2, sig3 :
      resolved_bit REGISTER ;
DISCONNECT sig1 : resolved_bit
      AFTER 5 ns ;
DISCONNECT OTHERS :
      resolved_bit AFTER 8 ns ;

bus_a and bus_b are declared as guarded signals of the type bus . During simulation the drivers for both signals are switched off with a delay of 6ns ( delay + 1 ns).

CONSTANT delay : time := 5 ns ;
SIGNAL bus_a, bus_b :
      resolved_zbit_vector32 BUS ;
DISCONNECT ALL : resolved_zbit_vector32
      AFTER delay + 1 ns ;

In the PACKAGE fourval a four-valued logic mvl4 and a corresponding vector are defined.

The function resolved is declared. Consequently a 'resolved signal' can be derived as a SUBTYPE .

In the PACKAGE BODY the function resolved is described.

• If the input signal choice changes to 1 the signal driver of the first block is activated and passes the first input signal on to the output after 20 ns.
• If choice changes to 2 the second block passes the second input signal on the output after 18ns.
• As the first signal driver switches off only after 25 ns both drivers are active simultaneously for 7ns. The resulting signal is determined by the 'resolution function' of the output signal.
• If choice changes to a value other than 1 or 2 the last active driver switches off after 25 ns and the output signal changes to its default value (in this case 'Z') as it is declared as a bus .
• If it were declared as a REGISTER the last signal value would be kept.

PACKAGE fourval IS
   TYPE mvl4 IS ('X','0','1','Z') ;
   TYPE mvl4_vector IS ARRAY
         (natural RANGE <>) OF mvl4 ;
   FUNCTION resolved (a: mvl4_vector)
         RETURN mvl4 ;
   SUBTYPE mvl4_r IS resolved mvl4 ;
END fourval ;
 
PACKAGE BODY fourval IS
   FUNCTION resolved (a: mvl4_vector)
         RETURN mvl4 IS
      VARIABLE result : mvl4 := 'Z' ;
      -- Defaultwert: 'Z'
   BEGIN
      ...
      RETURN result ;
   END resolved ;
END fourval ;
 
 
USE work.fourval.ALL ;
ENTITY mux_2_1 IS
PORT (in_signals : IN
   mvl4_vector (1 TO 2) ;
      choice     : IN integer ;
      out_signal : OUT mvl4_r BUS ) ;
END mux_2_1 ;
 
ARCHITECTURE with_guards OF mux_2_1 IS
   DISCONNECT out_signal : mvl4_r
              AFTER 25 ns ;
BEGIN
 
   choice_1 : BLOCK (choice = 1)
   BEGIN
     out_signal <= GUARDED
        in_signals(1) AFTER 20 ns ;
   END BLOCK ;
 
   choice_2 : BLOCK (choice = 2)
   BEGIN
      out_signal <= GUARDED in_signals(2)
            AFTER 18 ns ;
   END BLOCK ;
 
END with_guards ;