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6.5
Keypad, Display and SIM Interface
6.5.1 Keypad and Display
The keypad and display forms part of the logic board and consists of the following:
• Key switches (4 [N1]x 5 Matrix)
• LCD module (72 x 32 Graphical based display module)
• Back-Light illumination (10 green LED's, six for keys and four for the LCD)
• Indicator LED (Red/Green bicolour LED, to indicate charging and call status)
All control and I/O interface to the keypad and display is performed by the Nell
device.
The Key switches, LCD module, Backlights, Call / charger LED's and SIM interface
are shown in Figure 10d.
6.5.2 Keypad switches and Scanning
The key switches are metal domes which make contact between two concentric
pads on the top layer of the PCB when pressed. There are 18 switches (SW1-18),
connected in a matrix of 5 rows by four columns, as shown in fig 10d, except for
the power switch (SW20) which is connected independently. Two additional
momentary action push-button switches are mounted on a flexible PCB on the
side of the handset and connected to the row/column matrix by three gold pads
(SW21). These perform the volume "UP" and "DOWN" functions.
The row and column lines of the keypad are connected to ports on the ILB section
of Nell. The rows (KEYROW: 0-5) are inputs with 50kΩ pull-up resistors, while the
columns (KEYCOL: 0-3) are outputs. When a key is pressed, the corresponding
row and column are connected together, causing the row input to go low and
generate an interrupt. The columns/rows are then scanned by Nell to identify the
pressed key.
6.5.3 Display and Interface
Power to the LCD is controlled by NELL #N3 and can be switched on and off via
ILBPORT0 (LCDPWR). A high on this output powers the LCD; a low switches it off.
There is also the control output LCDCS which is also derived from NELL #N3, this
acts as the chip select enable for the LCD module. There is also a 20 way address
bus, which carries the address coding information for displaying graphical text
onto the LCD. In addition to the address bus there is also a 15-way data bus for
relaying display data to the LCD. The connections DE (Data Enable) and WE (Write
Enable) from NELL #H11/H14 perform data enable and write enable functions.
See Figure.10d: KeyPad, Display and SIM Interface
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