ericsson t2x (i2c-based)

ericsson a1018, t20, t28, and t29 displays are controlled using an i2c-based on-glass controller (exact model name unknown).

pinout for ericsson t2x displays 1 VLCD +6.4V (lcd power supply, 3 - 6.4V (?)) 2 VLOGIC +2.7V (logic power supply, 2.7 - 6V (?)) 3 SDA i2c-SDA 4 GND GND 5 SCLK i2c-SCLK annotations the model name of the controller is unknown. Berty's page states that it is based on Philips PCF8554 (but there are some differences) exact voltage ranges are unknown to me. i collected information about these on different places and put them together Berty's page states Vlcd = 6.4V and Vlogic = 2.7V. Rifer uses 5.8V for both, Vlcd and Vlogic in his project

pages vs. rows:

the display is organised in columns 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.

ericsson t28 display showing a test image	ericsson t28 display with output generated by graphlcd

i2c-displays only need two signal lines, SDA (data) and SCLK (clock). i used D0 and D1 to connect the display to the parallel port.

signals:

                       +----------------------------+
                       |         1 2 3 4 5          |
                       |         # # # # #          |
                       +------================------+
                       |                            |
                       |          rear view         |
                       |    connector is visible    |
                       |                            |
                       |                            |
                       +----------------------------+


    Signal name  PC            LCD     Signal name
    ----------------------------------------------------------
    Data 0       2              3      SDATA  i2c-SDA
    Data 1       3              5      SCLK   i2c-SCLK
    Ground      18              4      GND    Ground 
                --              1      VLCD   +6.4V (lcd power supply)
                --              2      VLOGIC +2.7V (logic power supply)

    

circuit:

part list:

    Part#   Type                Value                  Annotation
    ---------------------------------------------------------------------------------------
    R1-R2   Resistor            1 kOhm       
    R3      Resistor            eg. 150 Ohm            or higher value if display pixels are too weak
    IC1     Voltage Reg.        7805 (or similar) 
    C1      Capacitor           2.2 uF
    D1      Diode               1N4148 (or similar)
    

remarks:

• the power supply (which is based on a circuit by Rifer) shown above is only an example.
  two different voltages for V_lcd and V_logic may be better, but this power supply worked fine for me and was tested successfully on different PCs
• Rifer uses a resistor with 320 Ohm, i got better results with 150 Ohm (display was too dark (too much contrast) when using 320 Ohm)
• changing the voltage influences the contrast

as i2c-displays only need two signal lines, it may be driven using the serial port. also the power can be gained through it (so no extra power supply is needed!)

signals:

                       +----------------------------+
                       |         1 2 3 4 5          |
                       |         # # # # #          |
                       +------================------+
                       |                            |
                       |          rear view         |
                       |    connector is visible    |
                       |                            |
                       |                            |
                       +----------------------------+


    Signal name  PC            LCD     Signal name
    ----------------------------------------------------------
    TxD          3              1      VLCD   +6.4V (lcd power supply)
    TxD          3              2      VLOGIC +2.7V (logic power supply)
    DTR          4              3      SDATA  i2c-SDA
    GND          5              4      GND    Ground 
    RTS          7              5      SCLK   i2c-SCLK

    

circuit:

part list:

    Part#   Type                Value                  Annotation
    ---------------------------------------------------------------------------------------
    R1,R2   Resistor            10 kOhm       
    R3      Resistor            eg. 150 Ohm            or higher value if display pixels are too weak
    IC1     Voltage Reg.        7805 (or similar) 
    C1      Capacitor           2.2 uF
    D1      Diode               1N4148 (or similar)
    D2,D3   Zener-Diode         up to 5V               i didn't have 5V zener-diodes, so i used 4.7V
    

remarks:

• the circuit is based on a circuit by Rifer.
  modification: i do not connect SDA to CTS (as i don't query the i2c-acknowledge bit)
• Rifer uses a resistor with 320 Ohm, i got better results with 150 Ohm (display was too dark (too much contrast) when using 320 Ohm)
• changing the voltage influences the contrast

circuit described above	same, different angle

using the third parameter of serdisp_init(), driver specific options and custom wiring can be set.
common information about passing options and customisable wiring can be found in a separate document.

    examples:
    
      serdisp_init(sdcd, "ERICSSONT2X", "INVERT=YES");
      serdisp_init(sdcd, "E///T2X", "WIRING=SDA:D6,SCLK:D7");
    

  0 .. no delay
  1 .. one call of gettimeofday()
 >1 .. delay at least x nanoseconds