Basic electronics fundamentals – IV

Polling is a scheme or an algorithm to identify the devices interrupting the processor. Polling is employed when multiple devices interrupt the processor through one interrupt pin of the processor.

The polling can be classified into software and hardware polling. In software polling the entire polling process is govern by a program. In hardware polling, the hardware takes care of checking the status of interrupting devices and allowing one by one to the processor.

The interrupt controller is employed to expand the interrupt inputs. It can handle the interrupt request from various devices and allow one by one to the processor.

For synchronous data transfer scheme, the processor does not check the readiness of the device after a command have been issued for read/write operation. This scheme the processor will request the device to get ready and then read/Write to the device immediately after the request. In some synchronous schemes a small delay is allowed after the request.

In asynchronous data transfer scheme, first the processor sends a request to the device for read/write operation. Then the processor keeps on polling the status of the device. Once the device is ready, the processor execute a data transfer instruction to complete the process.

In handshake output operation, the processor will load a data to port. When the port receives the data, it will inform the output device to collect the data. Once the output device accepts the data, the port will inform the processor that it is empty. Now the processor can load another data to port and the above process is repeated.

The baud rate is the rate at which the serial data are transmitted. Baud rate is defined as l /(The time for a bit cell). In some systems one bit cell has one data bit, then the baud rate and bits/sec are same.

Interrupt is a signal send by an external device to the processor so as to request the processor to perform a particular task or work.

The input devices used in the microprocessor-based system are Keyboards, DIP switches, ADC, Floppy disc, etc.

The process of sending a zero to each row of a keyboard matrix and reading the columns for key actuation is called scanning. The scan time is the time taken by the processor to scan all the rows one by one starting from first row and coming back to the first row again.