Robotix Tutorial 8
- 1. 31 st Jan to 1 st Feb 2008 TECHNOLOGY ROBOTICS SOCIETY Indian Institute of Technology, Kharagpur
- 2. Computer Control Parallel & Serial Port Communication
- 3. 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
- 4. PC Parallel Port – Pin Layout
- 5. 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)
- 6. PC Parallel Port – I/O Registers - marked bits in register byte are unused
- 7. Accessing Parallel Port – VC ++ #include <conio.h> #define Data 0x378 // Base address #define Status 0x379 // Base address + 1 #define Control 0x37a // Base address + 2 int main () { unsigned char Bits; Bits = 0b11001010; _outp(Data, Bits); /* output data */ Bits = _inp(Status);/* input data */ return (0); }
- 8. 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
- 9. 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
- 10. Serial Port vs. Parallel Port Serial cables can be much longer that Parallel cables 50V swing compared to 5V swing Null Modem Configuration just needs 3 core cable compared to 19 core parallel port cable Serial suited for wireless transmission Microcontrollers just need two pins (RXD & TXD) for communication
- 11. Null Modem Configuration Pin 3 Transmit Data Pin 2 Receive Data Pin 5 Signal Ground Pin 4, 6, 1 shorted together Pin 7, 8 shorted together
- 12. RS-232 Waveforms Asynchronous Communication i.e. separate clock at both ends Frame synchronization done by the start / stop bit Line is kept logic 1 when idle. Start bit is logic 0 Bit order from LSB to MSB
- 13. RS-232 Level Converters For using the RS232 data, digital devices need TTL/CMOS voltage levels Level conversion is done using IC MAX232 / DS232
- 14. 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)
- 15. Accessing Serial Port - VB MSComm Control 6.0 is used for serial port communication
- 17. MSComm Control Properties Com Port identification number Settings: Baud Rate, Parity Check, Data Bits, Stop Bits Hand Shaking Method : Xon/Xoff for null-modem configuration
- 19. MSComm Control Properties InBufferSize : Input buffer size OutBufferSize : Output buffer size RThreshhold : Receive size for interrupt generation SThreshhold : Min. transmit size InputLen : Number of bytes to be picked up from the input buffer EOFEnable : Search for EOF character
- 21. MSComm Control Properties ParityReplace : Parity Error replacement character NullDiscard : Null characters sent to the receive buffer or not RTSEnable : Request to Send enable DTREnable : Data Terminal Ready
- 22. Example Code ‘ Receive Data Private Sub CommunicationTerminal_OnComm() Dim InputBuffer As String If CommunicationTerminal.CommEvent = comEvReceive Then InputBuffer = CommunicationTerminal.Input End If ‘ Use InputBuffer as per requirement End Sub ‘ Transmit Data If CommunicationTerminal.PortOpen = True Then CommunicationTerminal.Output = “Hello” End If