Standard Digital I/O Ports; Digital Input Port; Digital Output Port; Special Digital Port Functions - Conrad Electronic C- CONTROL 1 UNIT M 2.0 Hardware Manual

Standard digital I/O ports

The C-Control Computer provides two standard byteports (16 bitports, P1 to P16). Each bitport can be
used as input or output port. Both byteports are provided with software switchable pull up resistors
(30k). Each of the eight analog ports (A/D-converter) can be alternatively used as a standart digital
I/O port if this function is enabled in the configuration register. Each of this port can then be
considered as standard bitport (P17 to 24) but has no switchable pull up resistors. More details you
will find in the BASIC++ Manual.

Digital Input Port

Digital input ports are used to request an external switch status. A digital input is on undefined logical
level if nothing is connected (eg. an external switch is open) Therefore it is recommended to tie the
port to a defined level eg. conncting a pull up resistor to the port. In this case a closed switch causes
the port reading as „false" (logical lo level) and an open switch will be read as „true" (logical hi level )
After applying the operation voltage or after entering the reset state all ports are switched to inputs.

Digital Output Port

If a digital port is switched to output you can connect cicuits, transistors or LEDs with current limiting
resistors. The maximum load (output) current of each port must not exeed 10mA. In all cases a current
limit (e.g by connecting a resistor) has to be ensured. Otherwise a immediate and permanent damage
of ports can result. The port function ( if a port is input or output) is controlled during program
execution. After applying the operation voltage or after entering the reset state all ports are switched to
inputs.

Special Digital Port Functions

The operating system offers some special functions which occupy dedicated ports. This functions can
be used e.g. to drive IIC-Bus devices connected to port 9 and 10. More details regarding this point you
will find in the BASIC++ manual.

Analogports

The C-Control Computer offers you eight A/D ports and two D/A-ports (witch servo drive capabilities
as alternate function). The maximum input conversion range of the A/D-converters is fixed by the
applied reference voltage. The maximum output voltage of the D/A-converters is independent of the
reference voltage and always as high (and accurate) as the operating voltage.

Reference voltage

Before using the A/D-converters, the reference voltage has to be connected with the reverence
voltage input of the C-Control Computer. This voltage defines the maximum input voltage applied to
the A/D converters and will cause a A/D conversion result of 255. For the most applications the 5V
operating voltage is sufficient accurate and can directly be used as reference voltage. If more
precission is required, an external reference voltage can be applied to the Uref input. All
measurements of the A/D converters are related to GND

A/D Converter Ports

All kind of sensors may be connected to the A/D-ports, if they match the maximum A/D input voltage.
The A/D converters have 8 bit resolution i.e one digit corresponds to 19.6mV. Protect the A/D-ports
with a 10k serial resistor if the input voltage applied to the ports can exeed voltages above 5V. This
resistor will not affect the conversion accuracy and provides a over voltage protection up to 12V

D/A Converter Ports

The two 8 bit D/A converter are PWM (Pulse Width Modulated) converters. The output pulse consissts
of 256 seperate sections swiched to logic lo or hi related to value of the D/A conversion output. If a
conversion output of 128 is required, 128 sections are set to hi and the remaining 127 sections are
hold lo. This waveform is repeated at a rate of 1930Hz, each single section is of 2us width. To convert
this PWM signal into a true analog value a simple RC low pass filter is working fine. Attention has to
be paid to the remaining ripple (deviations from ac onstant output voltage, varying with tim) which
depend on the load, connected to the RC filter. For more precision an active circuit is recommended.
Driving lamps or LEDs with this PWM do not require a filter because the repetition rate is to fast to be
realised as flickering of light.