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? WHENÓï¾ä(WHEN/ELSE»òWITH/SELECT/WHEN) ? GENERATEÓï¾ä ? BLOCKÓï¾ä ʹÓÃÔËËã²Ù×÷·û

ÔËËãÀàÐÍ ÔËËã²Ù×÷·û NOT, AND, NAND,OR Âß¼­ÔËËã NOR, XOR, XNOR ²Ù×÷ÊýÀàÐÍ BIT, BIT_VECTOR, STD_LOGIC, STD_LOGIC_VECTOR STD_ULOGIC, STD_ULOGIC_VECTOR ËãÊõÔËËã·û ±È½ÏÔËËã·û ÒÆÎ»ÔËËã·û ²¢ÖÃÔËËã·û +, ¡ª, *, /, ** =, /=, <, >, <=, >= sll, srl, sla, sra, rol, ror &£¬(, , ,) INTEGER, SIGNED, UNSIGNED ÈÎÒâÊý¾ÝÀàÐÍ BIT_VECTOR STD_LOGIC, STD_LOGIC_VECTOR, STD_ULOGIC STD_ULOGIC_VECTOR, SIGNED, UNSIGNED WHENÓï¾ä WHENÓï¾äÊÇÒ»ÖÖ»ù±¾µÄ²¢·¢ÃèÊöÓï¾ä£¬ÓÐÁ½ÖÖÐÎʽ£ºWHEN/ELSEºÍWITH/SELECT/WHEN¡£ WHEN/ELSEÓï·¨½á¹¹£º assignment WHEN condition ELSE assignment WHEN condition ELSE ¡­; WITH/SELECT/WHENÓï·¨½á¹¹ WITH identifier SELECT assignment WHEN value, assignemnt WHEN value, ¡­;

µ±Ê¹ÓÃWITH/SELECT/WHENʱ£¬±ØÐë¶ÔËùÓпÉÄܳöÏÖµÄÌõ¼þ¸øÓ迼ÂÇ£¬Ê¹Óùؼü×ÖOTHERS£¬Èç¹ûÔÚijЩÌõ¼þ³öÏÖʱ²»ÐèÒª½øÐÐÈκβÙ×÷£¬ÄÇÓ¦¸ÃʹÓÃUNAFFECTED¡£ Àý£º

¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª-with WHEN/ELSE¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª- Output <= ¡°000¡± WHEN (inp = ¡®0¡¯ OR reset = ¡®1¡¯) ELSE ¡°001¡± WHEN ctl = ¡®1¡¯ ELSE ¡°010¡±;

¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¨Cwith WITH/SELECT/WHEN¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¨C WITH control SELECT

Output <= ¡°000¡± WHEN reset, ¡°111¡± WHEN set,

UNAFFECTED WHEN OTHERS;

¶ÔÓÚWHENÓï¾ä£¬WHEN valueµÄÃèÊö·½Ê½ÓÐÒÔϼ¸ÖÖ£º WHEN value ¨CÕë¶Ôµ¥¸öÖµ½øÐÐÅÐ¶Ï WHEN value1 to value2 ¨CÕë¶Ôȡֵ·¶Î§½øÐÐÅÐ¶Ï WHEN value1 | value2 | ¡­ ¨CÕë¶Ô¶à¸öÖµ½øÐÐÅÐ¶Ï GENERATEÓï¾ä

GENERATEÓï¾äºÍ˳ÐòÃèÊöÓï¾äÖеÄLOOPÓï¾äÒ»ÑùÓÃÓÚÑ­»·Ö´ÐÐijÏî²Ù×÷£¬Í¨³£ÓëFORÒ»ÆðʹÓá£Óï·¨½á¹¹ÈçÏ£º

label: FOR identifier IN range GENERATE (concurrent assignments) END GENERATE

GENERATEÓï¾ä»¹ÓÐÁíÒ»ÖÖÐÎʽ£ºIF/GENERATE£¬´Ë´¦²»ÔÊÐíʹÓÃELSE¡£IF/GENERATE¿ÉÒÔǶÌ×ÔÚFOR/GENERATEÄÚ²¿Ê¹Ó᣷´Ö®ÒàÈ»¡£ Label1: FOR identifier IN range GENERATE ¡­¡­

Label2: IF condition GENERATE (concurrent assignments) END GENERATE; ¡­¡­

END GENERATE; Àý£º

SIGNAL x: BIT_VECTOR(7 DOWNTO 0); SIGNAL y: BIT_VECTOR(15 DOWNTO 0);

SIGNAL z: BIT_VECTOR(7 DOWNTO 0); ¡­¡­

G1: FOR i IN x¡¯RANGE GENERATE z(i) <= x(i) AND y(i+8); END GENERATE;

GENERATEÖÐÑ­»·²Ù×÷µÄÉϽçºÍÏÂ½ç±ØÐëÊǾ²Ì¬µÄ£¬ÔÚʹÓùý³ÌÖл¹Òª×¢Òâ¶àÖµÇý¶¯ÎÊÌâ¡£ Àý£º

OK: FOR i IN 0 TO 7 GENERATE

Output(i) <= ¡®1¡¯ WHEN (a(i) AND b(i)) = ¡®1¡¯ ELSE ¡®0¡¯; END GENERATE;

¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª NotOK: FOR i IN 0 TO 7 GENERATE

accum <= ¡°1111_1111¡± WHEN (a(i) AND b(i)) = ¡®1¡¯ ELSE ¡°0000_0000¡±; END GENERATE;

¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª- NotOK: FOR i IN 0 TO 7 GENERATE Accum <= accum + 1 WHEN x(i) = ¡®1¡¯; END GENERATE;

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VHDLÖÐÓÐÁ½ÖÖBLOCK£ºsimple BLOCKºÍguarded BLOCK¡£ n Simple BLOCK

Simple BLOCK½ö½öÊǶÔÔ­ÓдúÂë½øÐÐÇøÓò·Ö¸î£¬ÔöÇ¿Õû¸ö´úÂëµÄ¿É¶ÁÐԺͿÉά»¤ÐÔ¡£Óï·¨½á¹¹ÈçÏ£º label£ºBLOCK [ declarative part] BEGIN

(concurrent statement) END BLOCK label;

¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª- ARCHITETURE example¡­ BEGIN ¡­

block1: BLOCK BEGIN

¡­

END BLOCK block1; ¡­

block2: BLOCK BEGIN ¡­

END BLOCK block2; ¡­

END example;

¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¨C Àý£º b1: BLOCK

SIGNAL a: STD_LOGIC; BEGIN

a <= input_sig WHEN ena = ¡®1¡¯ ELSE ¡®z¡¯; END BLOCK b1;

¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª- ÎÞÂÛÊÇsimple BLOCK»¹ÊÇguarded BLOCK£¬ÆäÄÚ²¿¶¼¿ÉÒÔǶÌׯäËûµÄBLOCKÓï¾ä£¬ÏàÓ¦µÄÓï·¨½á¹¹ÈçÏ£º label1: BLOCK

[¶¥²ãBLOCKÉùÃ÷²¿·Ö] BEGIN

[¶¥²ãBLOCK²¢·¢ÃèÊö²¿·Ö] label2: BLOCK

[ǶÌ×BLOCKÉùÃ÷²¿·Ö] BEGIN

[ǶÌ×BLOCK²¢·¢ÃèÊö²¿·Ö] END BLOCK label2;

[¶¥²ãBLOCKÆäËû²¢·¢ÃèÊöÓï¾ä] END BLOCK label1£»

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[ÉùÃ÷²¿·Ö] BEGIN

(ÎÀʽÓï¾äºÍÆäËû²¢·¢ÃèÊöÓï¾ä) END BLOCK label;

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[VARIABLE name type [range] [ := initial_value; ]] BEGIN

(˳ÐòÖ´ÐеĴúÂë) END PROCESS [label];

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IF (x < y) temp := ¡°1111_1111¡±;