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The following diode logic gates work in both active-high or active-low logic, however the logical function they implement is different depending on what voltage level is considered active. Switching between active-high and active-low is commonly used to achieve a more efficient logic design.
Diode–transistor logic (DTL) is a class of digital circuits that is the direct ancestor of transistor–transistor logic. It is called so because the logic gating functions AND and OR are performed by diode logic , while logical inversion (NOT) and amplification (providing signal restoration) is performed by a transistor (in contrast with ...
A family of diode logic and diode–transistor logic integrated circuits was developed by Texas Instruments for the D-37C Minuteman II Guidance Computer in 1962, but these devices were not available to the public. A variant of DTL called "high-threshold logic" incorporated Zener diodes to create a large offset between logic 1 and logic 0 ...
Some TTL logic parts were made with an extended military-specification temperature range. These parts are prefixed with 54 instead of 74 in the part number. [1]A short-lived 64 prefix on Texas Instruments parts indicated an industrial temperature range; this prefix had been dropped from the TI literature by 1973.
Although the 7400 series was the first de facto industry standard TTL logic family (i.e. second-sourced by several semiconductor companies), there were earlier TTL logic families such as: Sylvania Universal High-level Logic in 1963 [8] [9] [10] Motorola MC4000 MTTL [11] [12] [13] National Semiconductor DM8000 [14] [better source needed]
CTDL has two sets of logic level definitions: one for positive logic and the other for negative logic. There are both NPN (-6 to +6 supply, in+ out- logic) and PNP (-12 to 0 supply, in- out+ logic) flavors for gates. See page 84, 'CTDL - TWO WAY "AND" PNP'. The input logic levels are different than the output logic levels.
Open output is indicated on schematics with these IEEE symbols: [7] ⎐ – NPN open collector or similar output that can supply a relatively low-impedance low voltage when not turned off. Requires external pullup. Capable of positive-logic wired-AND connection. ⎒ – variant with internal pull-up resistor to provide a high voltage when off.
The same diode circuits are used, except a switch is placed in series with each diode. To read whether a switch is open or closed, the microcontroller configures one pin as an input with an internal pull-up resistor. The other pin is configured as an output and set to the low logic level.
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