Instructions

42Hardware

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 Atmega32 contains in its hardware an asynchronous serial interface according

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

tion of the interface. The application board contains a high value level conversion IC 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-magnetically loaded surround-

ings (e. g. in industrial applications) be induced in the interface cables and thus destroy connected

electrical circuits. By means of jumpers the data lines RxD and TxD can be connected to the Con-

troller PortD.0 and PortD.1. 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 RxD on Pin 3 and TxD on Pin 2. Pin 5 is the

GND connection. No handshake signals are being used for serial data transmission.

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.

Never connect the serial transmission outputs of two devices directly together! Transmission

outputs can usually be identified by their negative output voltage in quiescent condition.