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this page deals with connecting an pcd8544-based display to a parallel port and drive it using serdisplib
i'm not responsible for the content of external web pages
external web pages will generally open in separate browser windows or tabs
english is not my native language. please keep that in mind (corrections of english grammar and formulations are very welcome!)
email: mrwastl at users.sourceforge.net

pcd8544-based displays (+ compliant ones):

description

pcd8544-based displays can be found in some monochrome nokia-cellphones. with some technical skills, an independant, small display with background light can be gained out of these phones at hardly any costs.

specifications
resolution	84x48
colours	monochrome
controller	pcd8544
backlight	no, but with some skills the background light (4 to 6 LEDs, green) laying on the cellphone board can be used
adjustable contrast	yes, programmable
dimensions	`LPH7366`: module: 38.4 x 33 mm, display area: 29 x 19.5 mm (datasheet) `LPH7779`: module: 38.5 x 35 mm, display area: 30 x 22 mm (measured)
names in serdisplib	`PCD8544` ... generic for LPH7366, LPH7677, and LPH7779; no backlight ("`WIRING=1`") `LPH7366` ... LPH7366 only, with backlight support ("`WIRING=0`") examples: serdisp_init(sdcd, "PCD8544", ""); serdisp_init(sdcd, "LPH7366", "");

specifications LPH7690
resolution	90x60
colours	monochrome
controller	pcd8544 compliant commands
backlight	no
adjustable contrast	yes, programmable
dimensions
name in serdisplib	LPH7690 (example: `serdisp_init(sdcd, "LPH7690", "");` )

different display connector and board types

at least two different types of displays and circuit boards exist (i called them "type 1" and "type 2", maybe there are even more).

different display models
model name (of display)	type	nokia cellphones
LPH 7366	2	Nokia 5110, 5120, 5130, 5160, 6110, 6150
LPH 7677	1	Nokia 3210
LPH 7779	1	Nokia 3310, 3315, 3330, 3350, 3410
LPH 7690	1	Nokia 6210
further ones (list will be updated) ...

(digits in brackets show the marks in the following pictures)

type 1:
- the display is connected to the circuit board [2] using metallic pins [1]
- leds are soldered on the other side of the circuit board [3]
- they enlight the display through holes in the circuit board [3]
- the display has 8 pins
- pin #1 is rightmost (rear view of display, connectors at the bottom line)
- tiny cables could be soldered directly onto the metallic pins
- recommentation: design a circuit board for leds and display connector on your own because the circuit board can hardly be recycled
- update: some displays use a different method to connect the display module to the circuit board: contact pads and a separate "transmitter". it should be possible to solder wires directly onto the contact pads or to use an elastomer
type 2:
- the display is connected to the circuit board [2] using an elastomer ('lcd-connector' or 'rubber pad with conducting joints') [1]
- leds are soldered on the same side of the circuit board [3] underneath the position of the display
- on the other side of the circuit board there are no electronic parts
- the display itself is "clipped" [4] onto the circuit board
- the display has 9 pins (additional possibility to connect an external oscillator)
- pin #1 is rightmost (rear view of display, elastomer at the bottom line)
- the circuit board of the cellphone can be 'recycled' by simply cutting out the interesting part (see picture below)

different display types in bigger view + pin 1 positions

[pcd8544: where to cut the circuit board]

ad type 2: recycling the circuit board using a 'dremel' (or similar). red lines indicate where to cut through

ad type 2: i used a flex cable because i damaged the connector pad. as all leds are wired together, you only have to find two positions where to solder the wires so that the leds can be connected. i drilled two tiny holes through the circuit board (red arrows) and soldered a wire directly to a cathode and the other wire to an anode

some images


type 2 display finished and working	output generated by graphlcd

top ^

connecting a pcd8544-based display to the parallel port:

intro

the initial wiring is based on the wiring of an optrex 323 to the parallel port. as i didn't know of any other projects like this (with pcd8544-displays connected to the parallel port) i had to chose a wiring-'standard' for myself.

updates

2004-04-29: a severe mistake is now corrected: the pin-order was swapped in the photos (and at two positions in the description)!
when you look at the display in rear view with connectors at the bottom-line, pin 1 is rightmost (not leftmost)!
but: ascii arts in the source code of the library (serdisp_specific_pcd8544.h) did not contain this mistake!
2004-11-28: when reviewing the source code i noticed that signal 'CS' is never used and may be safely connected to GND. i updated circuits and descriptions to reflect this (CS slipped in from optrex323 when i adapted it's driver for pcd8544).
note: the functionality of serdisplib is NOT affected through this update (because CS wasn't used anyway)
2005-02-12: some pcd8544-based displays (especially newer ones) run unstable if Vout is not connected. inserting a capacitor avoids this. thanks to Michael Bülte for explaining this problem to me
added circuits using hardware reset (R/C-circuit) instead of /RES-wire

wiring

signals:

    Type 1 displays

                  +-------------------------+
                  |     1 2 3 4 5 6 7 8     |
                  |     # # # # # # # #     |
                  |  ===#=#=#=#=#=#=#=#===  |             1 .. VDD
                  +--=====================--+             2 .. SCLK
                  |                         |             3 .. SI
                  |                         |             4 .. D/C
                  |        rear view        |             5 .. /CS
                  |  connector is visible   |             6 .. GND
                  |                         |             7 .. Vout
                  |         LPH7779         |             8 .. /RES
                  |                         |
                  +-------------------------+


 Signal name  PC            LCD     Signal name
 ---------------------------------------------------------
 Data 0       2              3      SI   serial data input of LCD
 Data 1       3              2      SCLK serial clock line of LCD
 Data 2       4              4      D/C  (or sometimes named A0) command/data switch
 Data 5       7              8      /RES active low reset
 Data 7       9              -           Backlight (optional, not on display)
 Ground      18              6      GND  Ground for printer port and VDD
             --              1      VDD  +V (? mA) Chip power supply
             --              5      /CS   active low chip select (connected to GND)
             --              7      Vout output of display-internal dc/dc converter


 Type 2 displays


                  +--------------------------+
                  |     1 2 3 4 5 6 7 8 9    |
                  |     # # # # # # # # #    |             1 .. VDD
                  |  ===#=#=#=#=#=#=#=#=#==  |             2 .. SCLK
                  +--======================--+             3 .. SI
                  |                          |             4 .. D/C
                  |                          |             5 .. /CS
                  |        rear view         |             6 .. Osc
                  |   connector is visible   |             7 .. GND
                  |                          |             8 .. Vout
                  |         LPH7366          |             9 .. /RES
                  |                          |
                  +--------------------------+


 Signal name  PC            LCD     Signal name
 ---------------------------------------------------------
 Data 0       2              3      SI   serial data input of LCD
 Data 1       3              2      SCLK serial clock line of LCD
 Data 2       4              4      D/C  (or sometimes labelled A0) command/data switch
 Data 5       7              9      /RES active low reset
 Data 7       9              -           Backlight (optional, not on display)
 Ground      18              7      GND  Ground for printer port and VDD
             --              1      VDD  +V (up to 7.4 mA) Chip power supply
             --              5      /CS  active low chip select (connected to GND)
             --              6      Osc  external clock (connected to VDD)
             --              8      Vout output of display-internal dc/dc converter

circuits:

power supply for generating V+ needed by the following circuits

connecting 8-pin displays ('type 1') to the parallel port

connecting 9-pin displays ('type 2') to the parallel port

part list:

Part# Type Value Annotation
---------------------------------------------------------------------------------------
R1 Resistor eg. 270 Ohm
R2 Resistor eg. 330 Ohm
C1, C2 Capacitor some uF not mandatory, for smoothing input voltage
IC1 Var. Voltage Reg. LM317 (or similar) Vout should result in > 2.7V and <>

remarks:

type 2 displays (lph 7366) have 9 pins, type 1 displays (lph 7677, 7779) only have 8 pins. both circuits are illustrated above.

R7, R8, T1, D1 are needed in combination with LED background light only!

C1 and C2 are not mandatory, but at least C1 is recommended for smooth power supply.

C3 is only needed if the display runs unstable (possible erraneous effect: only every 2nd row is shown). thanks to Michael Bülte for this hint

R1 and R2 affect V_out of IC1 and are calculated using the following formula:
V_out = 1.25 * (1 + (R2 / R1))
usually (according to the data sheet of LM317) R1 should be 240 Ohm. i did not have such a resistor so i chose 270 Ohm. together with R2 = 330 Ohm i get V_out = 2.7777777 V.
that is at the lower limit of the specification of pcd8544. so maybe you should chose better values for R1 and R2.

i also tested a PJ 1084 (smd lowdrop adj. voltage reg.) as a replacement for the LM317 and it worked fine.
attention: different order of pins!

hardware reset vs. software reset:

to save one wire it is possible to replace the /RES-wire through a R/C-circuit.
part-list is the same as above with the following exceptions:
    Part#   Type                Value                  Annotation
 ---------------------------------------------------------------------------------------
 R3-R6   Resistor             1 kOhm    
 R7      Resistor            10 kOhm
 C4      Capacitor           10 uF

  

[pcd8544: circuit 8-pin displays with hardware reset]

8-pin displays ('type 1') with hardware reset

[pcd8544: circuit 9-pin displays with hardware reset]

9-pin displays ('type 2') with hardware reset

pro
one wire less
contra
display can no longer be reset by software

addressing

pages vs. rows:

the display is organised in colums and pages: 8 pixel-rows are combined to a so called page.
as only whole bytes can be transferred to the display, a single pixel cannot be changed without knowing its 7 'neighbour' pixels.
so a display buffer was introduced in the library. pixel changes are all done in this buffer and in a separate step only changed 'page bytes' are transferred (using an optimising algorithm) to the display.

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