Creative.chaos.de/LCD for WRAP

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Inhaltsverzeichnis 1 Preponderations 2 The DOG-module 3 The Circuitry 4 Wiring / Circuit Diagram 5 Assembly Manual 6 Parts List

Preponderations

Are there any suitable connectors on the WRAP?

• Connector "J2" - LPC-Expansion; citation from the WRAP-documentation: "The LPC port can be used to connect a super I/O device, or for an alternate flash EPROM to start with a corrupted or blank flash EPROM on board. These pins can also be reprogrammed as GPIO (not tested): Clear PMR pin multiplex register (I/O 09030h) bit 14 and 16, then set correct GPIO direction (input / output). Please see the SC1100 data sheet for details.

J2 Pin assignment:
==================

 1 PCLK2 LPC clock (33 MHz)
 2 GND ground
 3 LAD0 LPC data 0 (GPIO32)
 4 GND ground
 5 LAD1 LPC data 1 (GPIO33)
 6 GND ground
 7 LAD2 LPC data 2 (GPIO34)
 8 GND ground
 9 LAD3 LPC data 3 (GPIO35)
10 GND ground
11 LFRAME# LPC frame (GPIO37)
12 GND ground
13 PCIRST# reset (active low)
14 NC reserved
15 LPCISP high to use LPC flash, low to use on-board flash, pulled low by resistor
16 NC reserved
17 GND ground
18 V3 +3.3V supply
19 SERIRQ serial interrupt (GPIO39)
20 LDRQ# LPC DMA request (GPIO36)

There are these GPIO-pins on the Soekris boards as well. And there is an already working LCD with a Soekris, too. The WRAP offers 7 GPIOs - sufficient to run a display with 4 bits. (4 data, E, RW, RS). Expansions are then, however, impossible.

• I²C Bus

J3 Pin assignment
=================

1 +3.3V power supply
2 SCL1 I2C clock
3 SDA1 I2C data
4 GND ground

There are so called Bus-Expander for the I²C bus, these host 8 data pins. There was a discussion in the lcd4linux mailing list commenting the thing (mid 2005) as "pretty slow".

• USB (only with soldered-in USB expansion)

  To connect a device like that to USB, you'd have to invest somewhat more work. A developer of lcd4linux accepted the task of programming a microcontroller accordingly in order to get a LCD working.

• power issues

  - Pin 18 of J2 carries 3,3V. May carry strong currents (remark of the manufacturer)

  - The I²C also is supplied with 3,3V. May carry strong currents (remark of the manufacturer)

  - USB hosts 5V, max. 100mA - substantially lower in permanent operation (remark of the manufacturer)

The DOG-module

We chose a DOG (= Display On Glas) module by Electronic Assembly. It offers three different connection options and can be run with 3,3V. The RGB-illumination should be controlled by software.

• module options

  1x8 characters - 11,97mm, 2x16 characters - 5,57mm, 3x16 - 3,65mm

  backgound blue, yellow/green, black, white

• mechanical dimensions

  module: 27,94mm x 55mm (w x h), thickness 2mm (without) 5,8mm (with backlight)

• electrical data

  3,3V power supply

  250µA consumption

• connection options

  8bit data bus (impossible with the WRAP)

  4bit data bus (just so possible - 4bit data, E, RW und RS = 7 data pins)

  serial (very good - SI, CLK, RS und CSB = 4 data pins)

• backlight options

  white, yellow/green, blue, red, amber, coloured (rgb)

  remark of the manufacturer: Because of voltage tolerances, I discourage the use of white or blue backlights when using 3,3V. Amber, red and green should be ok.

The Circuitry

To be able to be more flexible on the number of data pins and to be able to use the possibilities of numerous displays, we decided to use a digital trick using shift registers.

A shift register allows us to run the display with 8 data bits (D0 ... D7). The second shift register supplies the control pins (E, RW, RS) for the display. The five remaining pins are free for other uses, i.e. to illuminate the RGB-backlight in 32 different colours...

2 bits of the GPIO-interface are connected with one serial-in pin of the shift register each.

1 bit of the GPIO goes to the clock pin.

1 bit is connected to both Output-Latch pins. This way, only valid (already shifted) data is signalled at the output pins.

Wiring / Circuit Diagram

Assembly Manual

Parts List

• LCD-Module

  (Reichelt) EA DOGM162W-A, 2x16 white or different colour

• Backlight

  (Reichelt) EA LED55X31-B, blue or different colour - they don't have RGB

  direct merchandise via lcd-module.de

• multipoint connector (female)

  (Reichelt BL 1X10G 2,54, 4 units

• Capacitors
• shift registers

  (Reichelt) 74HC 595, 8-bit shift register with Output-Latch and Serial Input, 2 units

• Connector cable
• PC prototyping board

  (Reichelt) HPR 50X100

• etc