S6B0708

64COM/128SEG GRAPHIC DRIVER FOR DOT MATRIX

LCD

16

DATA TRANSFER

To match the timing of the display data RAM and registering to that of the controlling microprocessor, S6B0708

uses an internal data bus and bus buffer. When the microprocessor reads the contents of display data RAM, the

data for the initial read cycle is first stored in the bus buffer (dummy read cycle). On the next read cycle, the data

is read from the bus buffer onto the microprocessor bus. At the same time, the next block of data is transferred

from RAM to the bus buffer. Otherwise, when the microprocessor write data to display data RAM, the data is

written to RAM after the falling edge of "E". Therefore, it is necessary to check busy flag to write or read the next

data. (refer to Figure 3, 4)

PAGE ADDRESS REGISTER

The 3-bit page address register provides the page address to display data RAM (refer to Table 4). The micro-

processor issues set page address instruction to change the page and to access another page.

COLUMN ADDRESS COUNTER

The column address counter is a 6-bit pre-settable counter that provides column address to display data RAM

(refer to Table 4). It is incremented by 1 automatically after execution of each read/write data instruction. The

column address counter loops the values 0 to 127, and it is independent of page address register. The ADC pin is

issued to change the relationship between RAM column address and display segment output.

DISPLAY START LINE REGISTER

The display start line register stores the line address of display data RAM that corresponds to the first (normally

the top) line (COM1) of liquid crystal display (LCD) panel. When displaying contents in display data RAM on the

LCD panel, 6-bit data (DB[5:0]) of the set display start line is latched in display start line register. latched data are

transferred to the line address counter just before COM1 is high, pre-setting the line address counter. The line

counter is then incremented on the display latch clock signal once for every display line. It is used for vertical

scrolling of the liquid crystal display screen.