DC instruction—Hexadecimal constant

Hexadecimal constants generate large bit patterns more conveniently than binary constants. Also, the hexadecimal values you specify in a source module let you compare them directly with the hexadecimal values generated for the object code and address locations printed in the program listing.

Each hexadecimal digit (see 1 in Table 1) specified in the nominal value subfield is assembled into four bits (their binary patterns can be found in Self-defining terms). The implicit length in bytes of a hexadecimal constant is then half the number of hexadecimal digits specified (assuming that a high-order hexadecimal zero is added to an odd number of digits). See 2 and 3 in Table 1.

An 8-digit hexadecimal constant provides a convenient way to set the bit pattern of a full binary word. The constant in the following example sets the first and third bytes of a word with all 1 bits.

         DS              0F
TEST     DC              X'FF00FF00'

The DS instruction sets the location counter to a fullword boundary. (See DS instruction.)

The next example uses a hexadecimal constant as a literal and inserts a byte of all 1 bits into the rightmost 8 bits of register 5.

         IC              5,=X'FF'

In the following example, the digit A is dropped, because 5 hexadecimal digits are specified for a length of 2 bytes:

ALPHACON DC              3XL2'A6F4E'         Generates 6F4E 3 times

The resulting constant is 6F4E, which occupies the specified 2 bytes. It is duplicated three times, as requested by the duplication factor. If it is specified as:

ALPHACON DC              3X'A6F4E'           Generates 0A6F4E 3 times

the resulting constant has a hexadecimal zero in the leftmost position.

0A6F4E0A6F4E0A6F4E

Table 1. Hexadecimal constants
Subfield	Value	Example	Result
1. Duplication factor	Allowed
2. Type	X
3. Type Extension	Not allowed
4. Program type	Allowed
5. Modifiers Implicit length: (length modifier not present)	As needed	`X DC X'FF00A2' Y DC X'F00A2'`	`L'X = 3` 2 `L'Y = 3` 2
Alignment:	Byte
Range for length:	1 to 256 (byte length) .1 to .2048 (bit length)
Range for scale:	Not allowed
Range for exponent:	Not allowed
6. Nominal value Represented by:	Hexadecimal digits (0 to 9 and A to F)	`DC X'1F' DC X'91F'`	Object code `X'1F'` 1 `X'091F'` 3
Enclosed by:	Apostrophes
Exponent allowed:	No
Number of values per operand:	Multiple
Padding:	With zeros at left
Truncation of assembled value:	At left