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introduction_to_digital_systems:realization_of_comb._logic [2023/03/27 11:31] mexleadmin |
introduction_to_digital_systems:realization_of_comb._logic [2023/09/19 23:48] (aktuell) mexleadmin |
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- | ====== 4. Realization of Combinatorial Logic ====== | + | ====== 4 Realization of Combinatorial Logic ====== |
===== 4.1 Preparation ===== | ===== 4.1 Preparation ===== | ||
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</ | </ | ||
- | It is simple to derive the gate logic from the formula (<imgref pic02>). For each of the three (min)terms, an AND-gate combines the needed inputs. As shown in the image, | + | It is simple to derive the gate logic from the formula (<imgref pic02> |
+ | For each of the three (min)terms, an AND-gate combines the needed inputs. | ||
+ | As shown in the image, the inverted inputs are usually | ||
<WRAP center> | <WRAP center> | ||
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==== 4.1.1 History of the Logic Families ==== | ==== 4.1.1 History of the Logic Families ==== | ||
- | A huge variety of integrated circuits (ICs) were used historically. <imgref pic03> shows two separate integrated circuits: There can be single or multiple gates in an IC with two or more inputs. The most used IC series was the 74xx ICs, where the xx are numbers that define the internal logic. | + | A huge variety of integrated circuits (ICs) were used historically. <imgref pic03> shows two separate integrated circuits: |
+ | There can be single or multiple gates in an IC with two or more inputs. The most used IC series was the 74xx ICs, where the xx are numbers that define the internal logic. | ||
<WRAP center> | <WRAP center> | ||
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The name TTL survived as a designation for the needed voltage levels $0V$ and $5V$. The $5V$ can still be found as supply voltage in some logic circuits. | The name TTL survived as a designation for the needed voltage levels $0V$ and $5V$. The $5V$ can still be found as supply voltage in some logic circuits. | ||
- | Modern controller logic is based on CMOS. <imgref pic04> shows that this type of logic only dissipates a fraction of the energy loss (and therefore heat) compared to the older logic families. This started the logic circuit development, | + | Modern controller logic is based on CMOS. <imgref pic04> shows that this type of logic only dissipates a fraction of the energy loss (and therefore heat) compared to the older logic families. This started the logic circuit development, |
The 74xx series is nowadays mostly from historical interest. Nearly all of the applications can now be done directly with microcontrollers. In rare cases, they are still used as "glue logic" between two logic ICs, e.g. for adjusting the logic voltage level. | The 74xx series is nowadays mostly from historical interest. Nearly all of the applications can now be done directly with microcontrollers. In rare cases, they are still used as "glue logic" between two logic ICs, e.g. for adjusting the logic voltage level. | ||
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==== 4.1.2 Logic Stages==== | ==== 4.1.2 Logic Stages==== | ||
- | From the <img pic02> we know what the logic for the sum-of-products looks like. in <imgref pic05> also the gate logic for the product-of-sums is shown. | + | From the <imgref |
Both consist of two logic stages: | Both consist of two logic stages: | ||
* For sum-of-products the first logic stage is set up with OR-gates, the second stage is the AND-gate, | * For sum-of-products the first logic stage is set up with OR-gates, the second stage is the AND-gate, | ||
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- | When there are programmable connections, | + | When there are programmable connections, |
- Programmable Array Logic (PAL): | - Programmable Array Logic (PAL): | ||
- Programmable Logic Element (PLE): the first stage is fixed, the second stage is programmable | - Programmable Logic Element (PLE): the first stage is fixed, the second stage is programmable | ||
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</ | </ | ||
- | In <imgref pic10> the simulation shows a PLE. in the top left corner the address is shown in decimal. The logic enables only the address '' | + | In <imgref pic10> the simulation shows a PLE. In the top left corner, the address is shown in decimal. The logic enables only the address '' |
<wrap # | <wrap # | ||
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PLA was often used as glue logic but is nowadays rarely in use. <imgref pic11> shows the principal setup. | PLA was often used as glue logic but is nowadays rarely in use. <imgref pic11> shows the principal setup. | ||
- | Based on PLAs - and in special | + | Based on PLAs - and especially |
< | < | ||
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* There are also **Field-Programmable Gate Arrays** (FPGA). These have a huge number (> | * There are also **Field-Programmable Gate Arrays** (FPGA). These have a huge number (> | ||
- | FPGAs can be used to test new microcontrollers and microchips. For this, the FPGA is configurated | + | FPGAs can be used to test new microcontrollers and microchips. For this, the FPGA is configured |
<WRAP center> | <WRAP center> |