LCD displays MUST be initialized .This is done in two ways.
One is by internal reset circuit and the other is by using commands.The
white text below is an extract from a Hitachi document.
by Internal Reset Circuit
An internal reset circuit automatically initializes the HD44780U
when the power is turned on. The
following instructions are executed during
the initialization. The busy flag (BF) is kept in the busy state
until the initialization ends (BF = 1). The busy state lasts
for 10 ms after VCC rises to 4.5 V.
DL = 1; 8-bit interface data
N = 0; 1-line display
F = 0; 5 ´ 8 dot character font
Display on/off control:
D = 0; Display off
C = 0; Cursor off
B = 0; Blinking off
Entry mode set:
I/D = 1; Increment by 1
S = 0; No shift
Sounds good ? Now
read this :
If the electrical characteristics conditions listed under the
table Power Supply Conditions Using
Internal Reset Circuit are not met, the internal reset circuit
will not operate normally and will fail
to initialize the HD44780U. For such a case, initialization must
be performed by Instruction.