i2c to keyboard interface.pdf

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I2C to Keyboard interface

Here follows a short description on how to use my i2c_kbd library, with this you could use

any AVR circuit with a matrix keyboard with minimal extra hardware. The interface from the

i2c to keyboard consists of a PCF8574 8bit I/O module, so with only 2 pins you could

interface the keyboard (or 3 pins if you use interrupt).

What you need to add in the beginning of your program is the following:

$lib "Key_i2c.lib"

$external _key_scan

Const Pcf8574_lcd = &H42

Config Scl = Portd.6

Config Sda = Portd.7

Dim _key_scan As Byte

!rcall _Key_init

.

.

.

!rcall _Key_Scan

if _key_scan = ? then …

If using interrupts add the following (skip last section from above):

Enable Interrupts

Config Int0 = Falling

On Int0 _int0_label

Enable Int0

.

.

.

if _key_scan = ? then …

.

.

.

_int0_label:

!rcall _Key_Scan

Return

The PCF8574 is connected as follows:

PCF8574

+5V

VDD

SDA

SCL

INT

P7

P6

+5V

A0

Hex adress 42

A1

A2

P0

P1

P2

P3

VSS

AVR- PortD.7

Gnd

AVR- PortD.6

AVR- INT0 (optional)

P5

Gnd

P4

C1 C2 C3 C4

A0, A1 and A2 gives the address

of the chip

A0 A1 A2 Pcf8574_lcd

0 0 0 &H40

1 0 0 &H42

0 1 0 &H44

1 1 0 &H46

0 0 1 &H48

1 0 1 &H4A

0 1 1 &H4C

1 1 1 &H4E

R1

R2

R3

R4

To observe when using interrupts!

Disable int0 before doing anything time consuming (RS232, LCD etc.) otherwise you may get

problem with those routines, when you press a key the program will jump to _key_scan.

The variable _key_scan holds the value of the key pressed (0 if none)

C1

C2

C3

C4

R1

1

2

3

4

R2

5

6

7

8

R3

9

10

11

12

R4

13

14

15

16

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