Preliminary Technical Information

AD6426

This Information applies to a product under development. Its characteristics and specifications are subject to change without notice. Analog Devices assumes no

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Revision Preliminary 2.3 (June 9, ´98)

- 19 -

Confidential Information

Keypad / Backlight / Display Interface

This interface combines all functions of display and keyboard

as shown in Table 10.

Table 10. Keypad / Backlight / Display Interface

Name

I/O

Function

KEYPADROW5 : 0

I

Keypad row inputs

KEYPADCOL3 : 0

O

Keypad column strobes

BACKLIGHT

O

Backlight control

DISPLAYCS

O

Display Controller chip

select

LCDCTL

O

LCD Control / Serial Display

Data Output

GPIO3

O

Serial Display Data Output

GPIO4

O

Serial Display Clock Output

By providing 4 keypad-column outputs (open drain, pull low)

and 6 keypad-row inputs the AD6426 can monitor up to 24

keys. Additionally, an extra column can be implemented by

using the “ghost column” method for a total of 30 keys. The

H8 processor is interrupted whenever a key is pressed. The

KEYPADCOL pins are connected to the Keypad Column3-0

flags in the KEYPAD COLUMN CC Control Register 9.

Bit

KEYPAD COLUMN CC Control Register 9

3 : 0

Keypad Column 3-0

The six KEYPADROW pins are connected to the Keypad Row

5-0 flags in the KEYPADROW CC Control Register 10.

Bit

KEYPADROW CC Control Register 10

5 : 0

Keypad Row 5-0

One backlight control output (BACKLIGHT) is provided,

which can be modulated to provide the same perceived

brightness for a reduced average current. Switching frequency

as well as duty cycle can be modified to compensate for

ambient lighting levels and changing battery voltage.

The BACKLIGHT output is activated by setting the

Backlight1 flag in the SYSTEM CC Control Register 0.

Bit

SYSTEM CC Control Register 0

5

Backlight 1

Once activated, an internal PWM circuit can control the

frequency and the duty cycle of the output signal. The PWM

circuit is enabled by the Modulate1 flag in the BACKLIGHT

CC Control Register 50. To switch the backlight continuously

on, enable the Backlight 1 flag and disable the Modulate 1

flag.

Bit

BACKLIGHT CC Control Register 50

2

Modulate 1

1: 0

Backlight LED Control (1:0)

The frequency is determined by the flags Backlight LED

Control (1:0) in the same register as shown in Table 11.

Table 11. Backlight Frequency

Bit 1

Bit 0

Frequency

0

0

6.3475 kHz

0

1

12.695 kHz

1

0

25.390 kHz

1

1

50.780 kHz

Duty cycle can be selected between 0 and 124/128 in 32 steps

of 4/128 by programming the Backlight Duty Cycle (4:0) flags

in the POWER CONTROL INTERNAL CC Control Register

44.

Bit

POWER CONTROL INTERNAL CC Control

Register 44

7 : 3

Backlight Duty Cycle (4:0)

The active period is determined according to the formula:

Active (high) Period =

Backlight Duty Cycle (4:0) × 4

128

The 6426 offers both parallel and serial interfaces for

connecting to LCD display controllers.

The parallel interface to a LCD controller is provided by two

dedicated control signals (LCDCTL and DISPLAYCS) and

parts of the address and data bus. A typical interface is shown

in Figure 5.

LCD

Controller

AD6426

DATA (15:8)

HWR

LCDCTL

ADD(0)

DISPLAYCS

DATA (7:0)

R/W

E

RS

CS

Figure 5. Parallel Display Interface

The on-chip control circuit automatically generates wait states

for interfacing to external display devices.