logic decoders and actuators
1 | address decoder |
2 | selector switch |
3 | 74LS258 selector |
o | an exercise in decoding a unique binary code so that an action may be performed when such a code is detected |
o | useful for a specific hardware module connected to a microprocessor address bus, so that this module is able to respond when it is addressed |
o | the address being decoded can be easily changed through the use of external inverters to make this black box a general-purpose one |
o | an exercise in selecting which input to present to the output |
o | this is in preparation for an understanding of the operation of the 74ls258, which has two 4-bit inputs to be, respectively, selected by the level ("1" or "0") that a selector pin is at |
o | the 258 selects whether "Counter A" or "Counter B" is displayed |
o | this can be used for viewing the time at a default selector pin position, or the alarm clock setting at the other selector pin position |
o | going beyond the alarm clock application, this is also be used to bring external binary bits into the computer printer port via its five input pins |
o | the cascading of selector chips for input data multiple bits is a "must" for computer interfacing projects |