Parallel Port Version with graphics display
This is the graphical parallel port Version.
It has 16 keys and a standard T6963 based graphical
LCD. (128*128 dots).
LCD and keys are directly connected to the PC's printer port (must be bidirectional)
and to a +5V supply, which can be 'borrowed' from a disk drive cable or
from the PC's keyboard socket.
Click to enlarge Image.
Inside view.
The display needs an additional backplane voltage of -10 to -15 Volt
This is generated from the main 5V supply by the inverter circuitry you
can see in the lower part of the image.
The inverter uses a MAX759CPD integrated adjustable power inverter from
Maxim http://www.maxim.ic.com
Click to enlarge Image.
Schematic.
The schematic contains 4 main parts:
1.) The 25 pin SUB-D connector to the PC's printer port.
2.) The LCD display with C1, R5 and a button as reset logic.
3.) The matrix keyboard with the pullup resistors R1-R4.
4.) The adjustable DC/DC converter around the MAX759.
Click to enlarge Image.
Discription:
Display
The display is a standard Hitachi T6963 controller based type.
Those types are available in a large amount of variations.
Not all have the same pin out as shown in the schematic.
Very often they have an additional nc (not connected) pin between
/Rst and D0.
If you by a display, be shure to get a data sheet or at least the pinout
of the interface connector.
The one I used has a resolution of 128*128.
It needs a +5V supply for the logic and an additional LCD backplane
voltage of -10 to -15 V.
This negative voltage is generated by the DC/DC converter circuit
around the MAX 759 Chip. If you have arlready have a stable negative
voltage, or your display has the converter integrated, you won't need this.
The display is directly connected to 8 data pins (D0-D7) and 4 control pins
(/select, init, /line_feed, /strobe) of the lpt port.
It shares 4 of the data pins (D0-D3) with the keypad.
This works because the data lines of the display can be disabled with
the /output_enable pin.
Reset logic
The T6963 needs a power on reset.
This is done by C2 and R5.
An additional button is connected across C2 to start a manual reset.
Keypad
The keypad consists of 16 buttons, arranged in a 4*4 matrix.
The rows are connected to the 4 data pins D0-D3.
The columns are connected to the 4 status pins: Select, Pe, /Ack and Busy.
Some PC's need pullup resistors at this input pins, some others don't.
Use them generelly or try it out.
To check for pressed keys, the software pulls down the data pins D0 - D3
one after another and checks the status pins wether one of them goes low.
The number of the pressed button is then computed by the row and column position.
DC/DC Converter
As said in the display section above, some display need an additional negative
backplane voltage of around -10 to -15V.
I used an integrated power converter chip from MAXIM to generate the negative
voltage.
Some tips for this part:
If you don't have a L-Meter and much RF experience, better use a premanufactured
conductor for L1. I made mine for myself and needed a whole evening to get the converter
to work.
The Schottky diode can be a 1N5818 or any other standard type you can find in an
old PC power supply.
You may have to vary R7 and R8, depending on the voltage your display needs.
Some words to the /SHDN input of IC1 and the DSPON output of the LCD module.
In order to prevent the display from DC current, the negative voltage must shut down
when the LCD controller T6963 goes into RESET or HALT mode. To achieve this, the
T6963 has a DSPON output pin that can be used to control the external DC/DC.
The MAX759 has a corresponding /SHDN pin that disables the output voltage.
Most displays dont have a DSPON output pin, so I connected the /SHDN directly to
DSPON pin at the T6963 chip. You can see this in the picture.
If you have a display with EL backlite, you'll need an additional supply voltage for it.
The voltage and power needed varies, so you may want to select a DC/DC converter
chip from MAXIM or any other supplier, that fits to your needs.
Connections
Connections from LPT to display and keypad, with pin descriptions:
LPT Keypad T6963
Pin Nr. Short Func. Pin Nr. Short Func.
---------------------------------------------------------------------
1 C0 /Strobe --------------- 7 /CE Chip enable
2 D0 Data0 --- Column1 --- 10 D0 Data0
3 D1 Data1 --- Column2 --- 11 D1 Data1
4 D2 Data2 --- Column3 --- 12 D2 Data2
5 D3 Data3 --- Column4 --- 13 D3 Data3
6 D4 Data4 --------------- 14 D4 Data4
7 D5 Data5 --------------- 15 D5 Data5
8 D6 Data6 --------------- 16 D6 Data6
9 D7 Data7 --------------- 17 D7 Data7
10 S6+ /ACK --- Row3
11 S7- Busy --- Row4
12 S5+ PE --- Row2
13 S4+ Select --- Row1
14 C1- /LF --------------- 6 /RD Read enable
15 S3+ /Error
16 C2+ /Init --------------- 5 /WR Write enable
17 C3- /Select --------------- 8 /C/D Command/Data
18 GND Ground --------------- 1 FG Frame ground
19 " " --------------- 2 Vss Ground
20 " "
21 " "
22 " "
23 " "
24 " "
25 " "
3 Vdd +5V
4 Vee -10..-15V
9 /Rst Reset
18 FS Font select
Software
Test software will follow in the next days.
This is the graphical parallel port Version.
Inside view.
Schematic.
