Computer Control : Computer Control Parallel & Serial Port Communication
PC Parallel Port - Features : PC Parallel Port - Features Commonly known as the printer port
25 pin D-Type connector
It has 12 digital output pins, 5 digital input pins
Pins operate at the TTL voltage level i.e. 0 – 5V
Port identified by a base address in the computer I/O memory space
PC Parallel Port – Pin Layout : PC Parallel Port – Pin Layout
PC Parallel Port – I/O Registers : PC Parallel Port – I/O Registers Most PC’s have 378 Hex base address
8 output pins are accessed via the DATA port (Base address)
4 output pins are accessed via the CONTROL port (Base address + 2)
5 input pins are accessed via the STATUS port (Base address + 1)
PC Serial Port - Features : PC Serial Port - Features Most commonly 9 pin D-Type connector. 25 pin D-Type is rare
Pins operate at -25 to + 25 voltage levels
Data transmitted as a bit sequence
Known as the EIA RS232C port or simply RS232
EIA RS232C Specifications : EIA RS232C Specifications Logic 0 is between +3 to +25 volts
Logic 1 is between -3 to -25 volts
-3 to +3 volts region is undefined
Maximum data rate of 19,600 bps
Serial Port vs. Parallel Port : Serial Port vs. Parallel Port Serial cables can be much longer that Parallel cables
50V swing compared to 5V swing
Serial suited for wireless transmission
Microcontrollers just need two pins (RXD & TXD) for communication
RS-232 Level Converters : RS-232 Level Converters For using the RS232 data, digital devices need TTL/CMOS voltage levels
Level conversion is done using IC MAX232 / DS232
RS-232 frame decoding : RS-232 frame decoding The decoding of the bit sequence frame is done by computer hardware
When communicating with robots, decoding done by onboard microcontroller
Microcontroller Serial communication interface is known as UART (Universal Asynchronous Receiver Transmitter)