Generating PORT Address for I/O Microprocessor and Interfacing by Ravinder Nath Rajotiya - October 12, 2021October 12, 20210 Generating the Ports for interfacing There are two techniques or methods for interfacing i/o devices, these are: i/o-Mapped I/O- In this method, the i/o device have separate address space and instructions exclusively for inputting or outputting the data from/to the devices. Instructions for reading/writing memory are different than i/o instructions.IN and OUT are used for i/o devices, and MOV is used for memory related operations. memory-mapped I/O- This techniques uses the common address space and instructions for communicating with the memory or the i/o. MOV instruction is used for i/o as well as memory related operations. In the following paragraph we will learn how to create the port addresses for the i/o-mapped i/o technique. We will use some address decoding logic gates for
8279 Keyboard/Display Interface Microprocessor and Interfacing by Ravinder Nath Rajotiya - April 5, 2020April 25, 20220 Keyboard Types Mechanical key switches Membrane type: with advantage that they can be made very thin and sealed Capacitive Type: When a key is pressed the capacitance between the plates varies. Hall effect: No mechanical contact. It take advantage of the deflection of a moving charge by a magnetic field. Keyboard Circuit connection and Interfacing Detect a key press De-bounce the key press Encode the valid key to produce a standard code for pressed key The above three tasks can be performed with hardware, software or a combination depending on the application Keyboard interfacing Figure show the interfacing of the keypad using 8255. The rows of the keypad are connected to say PORT-A and columns connected to PORT-B. PA is in