The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Chapter 8
(1) Write the number you want to display to data inputs B0-B3, and bring a digit-select input
(D1-D4) high to select the digit to write to. You can use the same XBY statement to do both.
For example, to write 7 to digit 2, use this statement: XBY(port address)=27H.
(2) With the data still on B0-B3, bring the digit-select input low. The data must remain on
B0-B3 for at least 200 nanoseconds after the digit-select input goes low. For step 1’s example,
you would write XBY(port address)=07H.
Follow the same procedure for each digit, and the TC7211 will continue to drive the
appropriate segments on all four digits. To change the value of a digit, repeat steps 1 and 2.
Displaying Messages
Sometimes a device has to display more complex messages than simple LEDs and 7-segment
displays can handle. For example, you might want to display messages like these:
Please enter your access code.
Select function:
Read
Program
Verify
Exit
Wind is from the west at 12 mph
Total cost = $5.82
With BASIC-52, you can use the host computer’s display, but this is no help if you want to
create a stand-alone project that doesn’t require a personal computer. In these situations, a
character-based dot-matrix LCD module is a solution.
These modules can display messages made up of numbers, characters of the alphabet, and
other symbols (for math functions, for example, or even symbols you design yourself).
Figure 8-8 illustrates. Devices that use this type of display include laser printers and test
equipment.
The Controller Chip
A special controller chip makes it easier to use LCD modules than you might think. Hitachi’s
HD44780 LCD controller is an 80-lead surface-mount chip that takes care of the details of
controlling the individual dots, or segments, on the display. For as low as $10, you can find
complete modules that contain an LCD panel and small circuit board containing the
138 The Microcontroller Idea Book