Hardware Reference
In-Depth Information
Figure 14.2
LCD controller (HD44780U or equivalent) instruction set.
Controller Instructions
The controller's instruction set is shown in
i gure 14.2, along with explanatory com-
ments and worst-case execution times. As mentioned above, a common design practice
is to adopt a slow clock to operate the LCD, such that any of the instructions has
enough time to be completed (so reading
BF
is not necessary); for example, 500 Hz,
hence allowing 2 ms for execution.
The maximum execution times in i gure 14.2 are for the controller's internal oscil-
lator operating at 270 kHz. This frequency is set by an external resistor between 75
k
(for
V
DD
= 5 V). If a different frequency is employed (with
different resistor values, the range that can be covered is roughly 100-500 kHz), then
the execution times must be multiplied by 270 kHz/
f
oscillator
.
Ω
(for
V
DD
= 3 V) and 91 k
Ω
