A floppy-disk controller ( FDC ) is a special-purpose chip and associated disk controller circuitry that directs and controls reading from and writing to a computer''''''''''''''''s floppy disk drive (FDD). This article contains concepts common to FDCs based on the NEC µPD765 and Intel 8272A or 82072A and their descendants, as used in the IBM PC and compatibles from the 1980s and 1990s. The concepts may or may not be applicable to, or illustrative of, other controllers or architectures.
A single floppy-disk controller (FDC) board can support up to four floppy disk drives. The controller is linked to the system bus of the computer and appears as a set of I/O ports to the CPU. It is often also connected to a channel of the DMA controller. On the x86 PC the floppy controller uses IRQ 6, on other systems other interrupt schemes may be used. The floppy disk controller usually performs data transmission in direct memory access (DMA) mode.
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Visual Logic provides a minimal-syntax introduction to essential programming concepts including variables, input, assignment, output, conditions, loops, procedures, arrays and files. Based on research that shows students have more success when they start by focusing on concepts rather than syntax, Visual Logic allows instructors to present material in a clear and illustrated manner. Programming fundamentals are covered in an appropriate problem-solving context, empowering rather than overwhelming the student.
The solution described here is nothing but a simple add-on, built around the 555 chip (IC1) wired in ‘freerunning’ mode. Modified configuration using the 1N4148 diode (D1) provides a control over duty cycle without changing the output pulse frequency. As a consequence, the output frequency of 555 remains unaffected while its duty cycle is varied over a wide range by the 100K brightness control potetntiometer (P1). Output of the 555 IC (pin 3) can be applied to the decoder’s blanking input through the 2N2222 driver transistor (T1).
Note: This is an unorthodox attempt to draw your attention to the working of 7-segment LED display driver ICs, especially their ripple blanking input/output (RBI/RBO) features. You can learn more about these less-known features by referring related articles/ tutorials/datasheets published elsewhere in this website/internet. As a bonus, you can build your own LED display brightness controller circuit using the ubiquitous 555 chip!