NEX ROBOTICS SPARK V ATMEGA16 Hardware Manual page 32

SPARK V ATMEGA16 Hardware Manual
The EN line is called "Enable" and it is connected to PC2. This control line is used to tell the
LCD that microcontroller has sent data to it or microcontroller is ready to receive data from
LCD. This is indicated by a high-to-low transition on this line. To send data to the LCD, program
should make sure that this line is low (0) and then set the other two control lines as required and
put data on the data bus. When this is done, make EN high (1) and wait for the minimum amount
of time as specified by the LCD datasheet, and end by bringing it to low (0) again.
The RS line is the "Register Select" line and it is connected to PC0. When RS is low (0), the data
is treated as a command or special instruction by the LCD (such as clear screen, position cursor,
etc.). When RS is high (1), the data being sent is treated as text data which should be displayed
on the screen.
The RW line is the "Read/Write" control line and it is connected to PC1. When RW is low (0),
the information on the data bus is being written to the LCD. When RW is high (1), the program
is effectively querying (or reading from) the LCD.
The data bus is bidirectional, 4 bit wide and is connected to PC4 to PC7 of the microcontroller.
The MSB bit (DB7) of data bus is also used as a Busy flag. When the Busy flag is 1, the LCD is
in internal operation mode, and the next instruction will not be accepted. When RS = 0 and R/W
= 1, the Busy flag is output on DB7. The next instruction must be written after ensuring that the
busy flag is 0.
Figure 3.29: LCD Timing Diagram.
LCD contrast and backlight setting
Contrast of the LCD can be adjusted by adjusting the potentiometer. To save power its backlight
can also be turned off by removing jumper J1. For jumper and potentiometer location, refer to
figure 3.27.
Figure 3.30: LCD schematics
© NEX Robotics Pvt. Ltd. and ERTS Lab IIT Bombay, INDIA 32