Z-World eDisplay OP7200, Руководство пользователя

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34 eDisplay (OP7200)
3.7 Liquid Crystal Display Controller
The LCD module controller chip (U2) and its associated SRAM (U1) provide support for
the LCD module. The controller chip is attached to the data bus on the OP7200’s Rabbit-
Core module, and is mapped to the I/O address space. This interface is composed of 8 data
bits, 1 address line, and 3 control lines (/IORD, /IOWR, and /LCDM-CS). Control regis-
ters within the controller chip can be accessed and data can be transferred to and from the
attached SRAM.
The SRAM interface consists of 16 address lines, 8 data lines, and 3 control lines.
The controller chip supports either 32K or 64K of SRAM. The OP7200 is designed using
a dual-footprint SRAM to accept either one 32K or one 128K byte part at U1. The 128K
part is standard. The full 64K supported by the controller is available with the 128K
SRAM, plus an additional 64K can be swapped in and out by using the programmed I/O
bit VA16. Pins 1–2 on header JP9 are normally connected by a 0
Ω
surface-mounted resis-
tor, but pins 2–3 should be connected instead for video SRAM paging with I/O bit VA16.
The third interface to the controller chip is to support the LCD module. This interface is
unidirectional. Data flow from the controller chip to the LCD module. A number of con-
trol lines are provided for this function, but not all of them are used for a particular LCD
module. The controller continually reads the SRAM for data placed there by the micropro-
cessor and refreshes the display periodically.
Other functions support the LCD module to adjust its contrast and to turn the white LED
backlight on and off.
A variable resistor between two of the LCD module’s terminals sets the contrast. U5 is a
digitally controlled potentiometer that can be controlled by software. Once the value is set,
the value will be maintained as long as power is maintained.
A single programmed I/O bit is used to turn the LED backlight on or off. Since this bit
does not have enough drive current to light the LED directly, it is buffered by the FET Q1.