Standard
The package STANDARD in library STD is part of the VHDL standard.
VHDL Source Of Package
package STANDARD is
type BOOLEAN is (FALSE, TRUE);
type BIT is ('0', '1');
type CHARACTER is (
NUL, SOH, STX, ETX, EOT, ENQ, ACK, BEL,
BS, HT, LF, VT, FF, CR, SO, SI,
DLE, DC1, DC2, DC3, DC4, NAK, SYN, ETB,
CAN, EM, SUB, ESC, FSP, GSP, RSP, USP,
' ', '!', '"', '#', '$', '%', '&', ''',
'(', ')', '*', '+', ',', '-', '.', '/',
'0', '1', '2', '3', '4', '5', '6', '7',
'8', '9', ':', ';', '<', '=', '>', '?',
'@', 'A', 'B', 'C', 'D', 'E', 'F', 'G',
'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',
'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W',
'X', 'Y', 'Z', '[', '\', ']', '^', '_',
' ', 'a', 'b', 'c', 'd', 'e', 'f', 'g',
'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
'p', 'q', 'r', 's', 't', 'u', 'v', 'w',
'x', 'y', 'z', '{', '|', '}', '~', DEL);
-- VHDL'93 includes all 256 ASCII characters
type SEVERITY_LEVEL is
(NOTE, WARNING, ERROR, FAILURE);
type INTEGER is range implementation_defined;
type REAL is range implementation_defined;
type TIME is range implementation_defined
units
fs;
ps = 1000 fs;
ns = 1000 ps;
us = 1000 ns;
ms = 1000 us;
sec = 1000 ms;
min = 60 sec;
hr = 60 min;
end units;
-- function that returns the current simulation time:
function NOW return TIME; --(VHDL'87)
subtype DELAY_LENGTH is TIME range 0 FS to TIME'HIGH;
impure function NOW return DELAY_LENGTH;
subtype NATURAL is INTEGER range 0 to INTEGER'HIGH;
subtype POSITIVE is INTEGER range 1 to INTEGER'HIGH;
type STRING is array (POSITIVE range <>) of CHARACTER;
type BIT_VECTOR is array (NATURAL range <>) of BIT;
type FILE_OPEN_KIND is
(READ_MODE, WRITE_MODE, MODE);
type FILE_OPEN_STATUS is
(OPEN_OK, STATUS_ERROR, NAME_ERROR, MODE_ERROR);
attribute FOREIGN: STRING;
end STANDARD;
Tips
The attribute FOREIGN can be attached to a procedure, function or
architecture to indicate that it is defined in a language other than VHDL
(usually C).
Generally it is better to use the types Std_logic and Std_logic_vector rather
than Bit and Bit_vector.
See Also
TEXTIO, Std_logic_1164, Package
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