4.9.9 Db Directive

The DB directive is used to initialize bytes of program memory.

The directive takes a comma-separated list of arguments. Each argument can be a numeric value (e.g., 55), a character constant (e.g. 'T'), or a string (e.g. "level" or 'level'). Each argument or each character of a string argument is written as one byte into consecutive program memory locations within the current psect.

The encoding of the values written depend on the delta flag of the psect that contains the directive. In the following code:

PSECT myBytes,class=CODE,delta=2
alabel:
  DB  ’X’,1,2,3,4,

the size of the address unit in the program memory specified by the delta psect flag (see 4.9.47.4 Delta Flag) is 2 bytes (true for Baseline and Mid-range PIC devices). In this case, the DB directive will initialize each word of program memory with the upper byte set to zero, specifically (in hexadecimal):

0058 0001 0002 0003 0004

However, on PIC18 devices, which uses program memory psects with the delta flag set to 1, no padding will occur. For the code:

PSECT myBytes,class=CODE,delta=1
alabel:
  DB  'X',1,2,3,4

the following (hexadecimal) data will be defined in the HEX file for the program memory.

58 01 02 03 04

Strings consist of a sequence of characters enclosed within either single or double quotes. There is no termination character added by the assembler. If you need a nul-terminated string, then specify the termination character as a separate argument to the DB directive, for example:

PSECT myConst,class=CODE,delta=1
bytes:
        DB "a terminated string",0

will define:

61 20 74 65 72 6D 69 6E 61 74 65 64 20 73 74 72 69 6E 67 00

The DB directive cannot be used to created objects in data memory. For that, use the DS directive (see 4.9.13 Ds Directive).