Important points to be noted for interface
This tutorial is taken from the book MY EXPERIENCE IN PARALLEL PORT INTERFACING. you can download it free from the files section(file:-parallelport(3 files) of yahoo group-booksbybibin http://groups.yahoo.com/group/booksbybibin/ comments about this book on www.booksbybibin.blogspot.com Important points to be noted for interface: 1.You have to make the port bidirectional before applying the external voltage to the data port because it can cause problem to your port (C5=1) 2.Don't remove the covering of the cable. If you are using Centronics pin as Female pin then take wire out of the pins shown above. Don't try to remove covering to take the wires out, because it can create problem of short-circuiting or you can solder the wires to a PCB. 3.proper delays must be used in inporting/outporting sequencially delay functions are defined in <time.h> delay(value); will halt the program execution for 'value' milliseconds, or you can apply looping by keeping it in a loop to produce delay. The need of delay is that Parallel Port has a speed of only 1MB/s, but your program execution speed is comparable to processor speed, so you should apply some delay between two port acess commands. But sometimes there is no need ( I got positive result by doing without delay better to put it). Usually we use parallel port speed about 1KB/sec(delay(1);) 4.don't try to draw power from parallel port. This cause damage to port. So it is necessary to use external power supply. 5.use only 74LS series IC's to interface between port and the other IC's because the Parallel Port is LS TTL ouputs and inputs. This is valid for inputting or outputting also. 6.switch on the circuit first then only connect the connector to the port 7.first disconnect the port then only switch off the circuit 8.don't forget to connect the ground of the port from the connector to the ground of the circuit. 9.Connect the ouput of the port to the input of the buffer and use the output of the buffer as the output of the port. Note: When you are inputting the port connect the wire to the input of a buffer and take the output of the buffer to the port. NOTE: use only 74LS buffer or 74LS IC's to the port directly. If you want to connect 40xx,45xx series IC's in the circuit it is better not to connect to the IC directly to the port. It is better to use buffer in between port and IC. 10. Don't connect motors or relays directly to parallel port. You are allowed to connect only normal digital IC's and transistor where driving current it low. Connect motors and relays using power transistors. 11.The data transfer speed of parallel port is 1MB/sec. 12. High Impedance state is considered as HIGH by parallel port That means if u doesn't connect any input and u apply inportting through port we get all high(a=255)(same as that of LS TTL gates). 13.If you use 74HC244 then it takes the high impedance state as LOGIC LOW but 74LS244 takes it as LOGIC HIGH. 14.BIOS settings is the main thing to note. Set BIOS to bidirectional port, if not available set it to any configuration except ECP,EPP,ECP+EPP 15.The external power supply must have the driving capability to drive the external circuit. You can use the SMPS of the computer you are working on. 16.Remember that all ports are registers, so they all keep the last data sent to the port 17. Don't extend the parallel port cable for long distance. If you want to use it for long distance use some buffer(74244) in after the length of the cable. Every cable has some resistance, capacitance and other factors and the voltage through printer cable is 5V, so if a HIGH is send from printer port, then it should reach HIGH for the circuit and this is possible only when you use the cable within limited length. If you see a serial port cable, you will get more length than parallel port cable because the HIGH for a serial port cable is -3V to -25V and LOW for 3 to 25V, so a good voltage swing is there and you can get good distance.
This tutorial is taken from the book MY EXPERIENCE IN PARALLEL PORT INTERFACING. you can download it free from the files section(file:-parallelport(3 files) of yahoo group-booksbybibin http://groups.yahoo.com/group/booksbybibin/ comments about this book on www.booksbybibin.blogspot.com Important points to be noted for interface: 1.You have to make the port bidirectional before applying the external voltage to the data port because it can cause problem to your port (C5=1) 2.Don't remove the covering of the cable. If you are using Centronics pin as Female pin then take wire out of the pins shown above. Don't try to remove covering to take the wires out, because it can create problem of short-circuiting or you can solder the wires to a PCB. 3.proper delays must be used in inporting/outporting sequencially delay functions are defined in <time.h> delay(value); will halt the program execution for 'value' milliseconds, or you can apply looping by keeping it in a loop to produce delay. The need of delay is that Parallel Port has a speed of only 1MB/s, but your program execution speed is comparable to processor speed, so you should apply some delay between two port acess commands. But sometimes there is no need ( I got positive result by doing without delay better to put it). Usually we use parallel port speed about 1KB/sec(delay(1);) 4.don't try to draw power from parallel port. This cause damage to port. So it is necessary to use external power supply. 5.use only 74LS series IC's to interface between port and the other IC's because the Parallel Port is LS TTL ouputs and inputs. This is valid for inputting or outputting also. 6.switch on the circuit first then only connect the connector to the port 7.first disconnect the port then only switch off the circuit 8.don't forget to connect the ground of the port from the connector to the ground of the circuit. 9.Connect the ouput of the port to the input of the buffer and use the output of the buffer as the output of the port. Note: When you are inputting the port connect the wire to the input of a buffer and take the output of the buffer to the port. NOTE: use only 74LS buffer or 74LS IC's to the port directly. If you want to connect 40xx,45xx series IC's in the circuit it is better not to connect to the IC directly to the port. It is better to use buffer in between port and IC. 10. Don't connect motors or relays directly to parallel port. You are allowed to connect only normal digital IC's and transistor where driving current it low. Connect motors and relays using power transistors. 11.The data transfer speed of parallel port is 1MB/sec. 12. High Impedance state is considered as HIGH by parallel port That means if u doesn't connect any input and u apply inportting through port we get all high(a=255)(same as that of LS TTL gates). 13.If you use 74HC244 then it takes the high impedance state as LOGIC LOW but 74LS244 takes it as LOGIC HIGH. 14.BIOS settings is the main thing to note. Set BIOS to bidirectional port, if not available set it to any configuration except ECP,EPP,ECP+EPP 15.The external power supply must have the driving capability to drive the external circuit. You can use the SMPS of the computer you are working on. 16.Remember that all ports are registers, so they all keep the last data sent to the port 17. Don't extend the parallel port cable for long distance. If you want to use it for long distance use some buffer(74244) in after the length of the cable. Every cable has some resistance, capacitance and other factors and the voltage through printer cable is 5V, so if a HIGH is send from printer port, then it should reach HIGH for the circuit and this is possible only when you use the cable within limited length. If you see a serial port cable, you will get more length than parallel port cable because the HIGH for a serial port cable is -3V to -25V and LOW for 3 to 25V, so a good voltage swing is there and you can get good distance.