Instructions

52Hardware

I2C Interface

Through this interface serial data can be transmitted at high speed. To do this only two signal lines

are necessary. Data transmission takes place according to the I2C protocol. To effectively use this

interface special functions are provided (see Software Description I2C).

I2C SCL

I2C Bus Clock Line

PortD.0

I2C SDA

I2C Bus Data Line

PortD.1

Power Supply (POWER, 5 Volt, GND)

Power is provided to the application board by means of a 9V/ 250mA Mains Plug-in Power Supply.

Depending on additionally used components it may later become necessary to use a power supply

with higher power rating. A fixed voltage control generates an internally stabilized 5V supply voltage.

This voltage is provided to all circuit components on the application board. Due to the power reserve

of the Plug-In Power Supply this voltage can also be used to power external ICs.

Please observe the Maximum Drawable Current. Exceeding this current may lead to immediate

destruction! Because of the relativelly high current consumption of the application board in the vicin-

ity of 125mA it is not recommended for use in devices consistently battery operated. Please see the

note on short time breakdowns of the power supply (see Reset Characteristics).

If you turn the application board to a position where the interface connectors (USB and serial)

show to the upper side, the leftmost column on the breadboard is GND and the rightmost column is

VCC.

Serial Interfaces

The Micro Controller Atmega128 contains in its hardware two asynchronous serial interfaces accord-

ing to RS232 standards. The format (Data Bits, Parity Bit, Stop Bit) can be determined during initial-

ization of the interface. The application board contains a high value level conversion IC for both inter-

faces to transform the digital bit streams to Non Return Zero Signals in accordance with the RS232

standards (positive voltage for low bits, negative voltage for high bits). The level conversion IC makes

use of an improved protection against voltage transients. Voltage transients can in electro-magnetic-

ally loaded surroundings (e. g. in industrial applications) be induced in the interface cables and thus

destroy connected electrical circuits. By means of jumpers the data lines RxD0 (PortE.0), TxD0

(PortE.1) and RxD1 (PortD.2), TxD1 (PortD.3) can through the Controller be connected to the level

converter. During quiescent condition (no active data transmission) a negative voltage of several volts

can be measured on Pin TxD against GND. RxD is of high impedance. The 9 pole SUB-D socket of

the application board carries RxD0 on Pin 3 and TxD0 on Pin 2. Pin 5 is the GND connection. No

handshake signals are being used for serial data transmission. The second serial interface is lead to

a 3 pole pin strip. Here RxD1 occupies Pin 2, TxD1 occupies Pin 1 while Pin 3 is GND.

The cable with connection to the NRZ Pins TxD, RxD and RTS may have a length of up to 10

meters. It is recommended to use shielded standard cables. When using longer lines or non-shiel-

ded cables interferences may detract correct data transmission. Only use cables of which the pin

assignments are known.