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EDE700 Serial LCD Interface IC
EDE700
0=2400,1=9600
0=Inverted,1=Standard
0=Diagnostic Mode
Connect to +5V DC
Digital Ground
LCD Enable Line
LCD RS Line
LCD RW Line
No Connection
1
2
3
4
5
6
7
8
9
BAUD
POLARITY
TEST
+5V
GND
Enable
RS
RW
N/C
XMIT
RCV
OSC1
OSC2
+5V
D7
D6
D5
D4
18
17
16
15
14
13
12
11
10
Serial Transmit
Serial Receive
Oscillator Connection
Oscillator Connection
Connect to +5V DC
LCD Data Pin 7
LCD Data Pin 6
LCD Data Pin 5
LCD Data Pin 4
The EDE700 Serial LCD Interface IC is designed to conveniently control text-based LCD modules via
a simple two or three wire link. This IC allows both engineer and hobbyist alike to easily
incorporate a LCD module into their design using a minimal amount of I/O lines. The EDE700
allows full LCD control, including the creation of custom characters. Also, in addition to the usual
sideways-scrolling feature standard on most LCD modules, the EDE700 is also capable of shifting text
from the bottom row of a 2-row LCD to the top row using only one command. 2400 or 9600 Baud
rates and selectable serial data polarity allow the EDE700 to communicate easily with most serial
devices. Connection to most microcontrollers, stamps, or microprocessors can be made using a
single data wire, without any type of voltage level conversion. Connection to a PC can be made
using only a 33KΩ resistor.
Some of the special features of the EDE700 are as follows:
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RS232 and TTL-level compatible
Single-chip design allows for easy system integration
Compatible with most 1x8 to 2x40 character HD44780 controlled LCDs
Useable with LCDs having either 1x14 or 2x7 connector configuration
Allows direct control of all LCD functions
Adds new "Row Shift-up" capability
Selectable data polarity eliminates necessity of RS-232 voltage converter
Data Read Mode allows screen data to be read back to host system
2400/9600 Baud data rates
Special Diagnostic Mode tests screen hookup and data transmission
Available in 18 pin DIP or SOIC packages
Copyright
©
1997 E-Lab Digital Engineering, Inc. All Rights Reserved.
Page 1
PIN DEFINITIONS
LCD Connection Pins
LCD Enable Line (Pin 6): .......................................
LCD Enable line;
pin 6 on LCD screen module
LCD RS Line (Pin 7):..............................................
LCD Register Select line;
pin 4 on LCD screen module
LCD RW Line (Pin 8):............................................
LCD Read/Write line;
pin 5 on LCD screen module
D4 (Pin 10): ..........................................................
LCD Data 4 line;
pin 11 on LCD screen module
D5 (Pin 11): ..........................................................
LCD Data 5 line;
pin 12 on LCD screen module
D6 (Pin 12): ..........................................................
LCD Data 6 line;
pin 13 on LCD screen module
D7 (Pin 13): ..........................................................
LCD Data 7 line;
pin 14 on LCD screen module
EDE700 Control & Data Pins
BAUD (Pin 1): .......................................................
Baud Rate Selection;
0 = 2400, 1 = 9600 Baud
Polarity (Pin 2): .....................................................
Serial Data Polarity Control;
0 = Inverted, 1 = Standard
Test (Pin 3):...........................................................
Diagnostic Mode;
0 = Test Mode, 1 = Normal Operation
RCV (Pin 17): ........................................................
Serial Data Input
XMIT (Pin 18):.......................................................
Serial Data Output (Normally unused)
Clock/ Power Pins
OSC1,OSC2 (Pin 16, Pin 15):................................
20 MHz Resonator Connection
+5V Power (Pin 14, Pin 4): ..................................
Connect to +5V DC
Ground (Pin 5): .....................................................
Connect to 0 VDC (GND)
PC CONNECTION
The EDE700 can be used with most HD44780-based text LCD's. The two most common types of
connectors on these modules are the 1x14 and 2x7 pin arrangements (there may be two additional
pins if the LCD is the backlit type). The pin numbers should be identified on the LCD module. Refer
to Figure One for connection of the LCD module to the EDE700. Notice that not all of the LCD
module's pins need to be connected, as the EDE700 uses a 4-bit transfer mode.
Figure One also illustrates the hookup used for connection to a PC. A RS-232 voltage-level converter
IC such as the MAX232 is not required; internal clamping diodes on the EDE700 convert the
incoming RS-232 level voltages into TTL-level signals. Also, notice that the POLARITY input on the
EDE700 is tied low; this causes the EDE700 to interpret the inverted RS-232 signals correctly (a
voltage-converter IC such as the MAX232, inside the PC, inverts the signal during transmission).
* IMPORTANT NOTE:
The 33KΩ resistor must be used when connecting to a PC in this fashion;
omitting it will cause excessive current to flow, possibly damaging both the PC serial port and the
EDE700 IC.
Copyright
©
1997 E-Lab Digital Engineering, Inc. All Rights Reserved.
Page 2
Figure One: Connection of EDE700 to a PC using only a 33KΩ Resistor
Ω
A 20MHz resonator is used to clock the EDE700. Alternately, you may choose to use a 20MHz
crystal or a 20MHz TTL oscillator. If you choose the latter, connect the oscillator output to only
OSC1 (Pin 16). The LCD contrast is set by a 10-20KΩ potentiometer. If the LCD screen will be used
in a relatively temperature-constant environment with a fixed viewing angle, you may choose to
replace this potentiometer with two suitably-valued resistors connected in series. The contrast pin
should be connected between the two resistors (use a potentiometer to first determine the
appropriate resistance values for your particular LCD).
The above schematic can be easily tested using the following QBASIC code (both the compiled and
the text version are available on E-Lab's web site):
REM Open channel to COM2 at 9600 Baud
OPEN "com2:9600,n,8,1,cd0,cs0,ds0,op0,rs" FOR OUTPUT AS #1
REM Clear Display
OUT &H2F8, &HFE
GOSUB 999
OUT &H2F8, &H1
GOSUB 999
REM Write first row of text to LCD screen
PRINT #1, "EDE700 Test Screen";
GOSUB 999
REM Jump to second row on 2 line LCD
OUT &H2F8, &HFE
GOSUB 999
OUT &H2F8, &HC0
GOSUB 999
REM Write second row of text to LCD screen
PRINT #1, "Time is: "; TIME$;
END
REM Adjust delay value according to PC speed.
REM 50000 is for Pentium; XT would use much lower figure
999 FOR delay = 1 TO 50000: NEXT delay
RETURN
Notice that the above code uses the COM2 port; to use the COM 1 port modify the "OPEN" line to
read "COM1" instead and also change the address &H2F8 to &H3F8 on the "OUT" lines.
Copyright
©
1997 E-Lab Digital Engineering, Inc. All Rights Reserved.
Page 3
DIAGNOSTIC MODE
When initially connecting the EDE700, you may wish to verify that you have the EDE700 to LCD
screen interface correctly wired prior to connecting the controlling device (PC, microcontroller, etc.).
A special diagnostic mode has been built into the EDE700 for this purpose.
Connect the LCD screen as illustrated in Figure One. The PC connection may be left undone for
now. Before turning on power to the circuit, connect the EDE700's TEST Pin (Pin 3) to Ground
instead of +5V. This will instruct the EDE700 to power up in Diagnostic Mode. When you apply
power, the message "EDE700 Version 1.00,N-8-1 (C) E-Lab, Inc" should appear on your display
screen (assuming your screen is wide enough to view the entire message). If this message appears
on your screen, the LCD module is connected correctly to the EDE700. If it does not appear, turn
the power off and double-check your wiring, including LCD module power and ground. (Don't
forget to try adjusting your contrast potentiometer - the display contrast might be the only problem!)
If you can't find the problem, consult the manufacturer's datasheet for your particular LCD module.
Although unlikely, it may have a custom pinout. The EDE700 will work with most any LCD module
that utilizes the HD44780 controller.
In addition to displaying the above message on the screen, starting the EDE700 in Diagnostic Mode
also causes a stream of "A"s to be sent out the Serial Transmit pin (Pin 18). This allows the
connection of the serial data stream from the EDE700 back to the host to be verified. This
connection is not necessary for ordinary operation and should only be connected if LCD screen data
will need to be read back from the LCD display module. Ordinarily, just two pins from the EDE700
will be connected to the host system - Serial Receive (Pin 17) and Ground (Pin 5).
CONNECTION TO OTHER SYSTEMS
The EDE700 can be connected to a variety of host controllers other than a PC, including the BASIC
Stamp™ series, numerous microcontrollers, or a microprocessor system. The type of connection used
is determined by the communications level voltage of the host system. For instance, the PC serial
port transmits using voltages ranging from -15 to +15 VDC. The schematic in Figure One relies on
the EDE700's internal input-clamping diodes to reduce the signal's voltage to TTL-levels. The 33KΩ
resistor is necessary to limit the current through these diodes. Because the voltage driver inside the
PC contains a level inverter, we use the EDE700 in "Inverted Mode" (Pin 2 Low). This causes the
EDE700 to transmit and receive using a polarity-inverted serial data stream.
If you do choose to use a voltage-converter IC such as the MAX232 (for instance, if the host is
separated from the EDE700 by a considerable distance), do not also use the 33KΩ resistor. Since the
MAX232 Level Shifter IC contains an inverter, the EDE700 should, when used in this configuration,
be operated in "Standard Mode" (Pin 2 High). In addition, if the EDE700 is to write data back to the
PC (used only when LCD character data needs to be read from the LCD screen), you must use the
MAX232 or similar voltage level converter to generate the RS-232 signal voltages that the PC needs
to operate properly. Again, in this case, operate the EDE700 in "Standard Mode". Data Readback
Mode used with stamps or microcontrollers, however, does not require the use of a level-converter
IC, as can be seen in Figure Three.
Connection to a BASIC Stamp™ or microcontroller requires no voltage level shifter or current-limiting
resistor, simply connect the microcontroller's serial output to the EDE700's Serial Data Input (Pin 17).
Depending upon the length of the data line, you may need to pull this line high using a 4.7KΩ
resistor, as shown in Figure Two. If your design needs to read data back to the host microcontroller
from the LCD, connect the EDE700's Serial Data Output (Pin 18) to the microcontroller's serial data
input. Typically, an arrangement such as this would use the EDE700 in "Standard Mode" (serial data
not inverted). Figure Two illustrates the connection of a BASIC Stamp™ I to the EDE700. Notice that
Copyright
©
1997 E-Lab Digital Engineering, Inc. All Rights Reserved.
Page 4
only one I/O pin is required to display text on the LCD screen. For this example, the EDE700 is set
to 2400 Baud (Pin 1 Low), Standard Polarity (Pin 2 High).
Figure Two: Connection of EDE700 to BASIC Stamp™ I
The following software, written for the BASIC Stamp™ I, will output text on both lines of a two-line
LCD. Notice that a "Pause 10" instruction is added after each write to the LCD internal control to
allow time for the LCD to execute the instruction.
REM Delay while LCD powers up...
PAUSE 500
REM Clear display and home cursor
SEROUT 7,T2400,($FE)
SEROUT 7,T2400,($01)
PAUSE 10
SEROUT 7,T2400,("Hello World...")
REM Move to start of second row
SEROUT 7,T2400,($FE)
SEROUT 7,T2400,($C0)
PAUSE 10
SEROUT 7,T2400,("This text should be on the second row!")
The following section outlines the use and function of the EDE700 LCD controller. While this
datasheet explains many of the specific LCD module features, your particular module may be slightly
different. When in doubt, always refer to the datasheet for your particular LCD module. In addition,
we have found that some one-line LCD modules do not have the entire row mapped contiguously in
memory; you may have to move the cursor position to the start of the LCD memory's "second line"
in order to write to the last half of the characters on a one-line display.
Copyright
©
1997 E-Lab Digital Engineering, Inc. All Rights Reserved.
Page 5

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