Interfacing the Standard Parallel Port | Interfacing the Standard Parallel Port http cpeacock Interfacing the Standard Parallel Port Disclaimer While every effort has been made to make sure the information in this document is correct the author can not be liable for any damages whatsoever for loss relating to this document. Use this information at your own risk. Table of Contents Introduction to Parallel Ports Page 1 Hardware Properties Page 2 Centronics Page 4 Port Addresses Page 4 Software Registers - Standard Parallel Port SPP Page 6 Bi-directional Ports Page 8 Using The Parallel Port to Input 8 Bits. Page 9 Nibble Mode Page 11 Using the Parallel Port s IRQ Page 12 Parallel Port Modes in BIOS Page 14 Parallel Port Modes and the ECP s Extended Control Register Page 15 Introduction to Parallel Ports The Parallel Port is the most commonly used port for interfacing home made projects. This port will allow the input of up to 9 bits or the output of 12 bits at any one given time thus requiring minimal external circuitry to implement many simpler tasks. The port is composed of 4 control lines 5 status lines and 8 data lines. It s found commonly on the back of your PC as a D-Type 25 Pin female connector. There may also be a D-Type 25 pin male connector. This will be a serial RS-232 port and thus is a totally incompatible port. Newer Parallel Port s are standardized under the IEEE 1284 standard first released in 1994. This standard defines 5 modes of operation which are as follows 1. Compatibility Mode. 2. Nibble Mode. Protocol not Described in this Document 3. Byte Mode. Protocol not Described in this Document 4. EPP Mode EnhancedParallel Port . 5. ECP Mode Extended Capabilities Port . The aim was to design new drivers and devices which were compatible with each other and Interfacing the Standard Parallel Port Page 1 Interfacing the Standard Parallel Port http cpeacock also backwards compatible with the Standard Parallel Port SPP . Compatibility Nibble Byte modes use just the
