dan333
November 12, 2013, 4:42am
12
Wired-AND diode ckt:
A wired logic connection is a logic gate that implements boolean algebra (logic) using only passive components such as diodes and resistors. A wired logic connection can create an AND or an OR gate. Limitations include the inability to create a NOT gate, the lack of amplification to provide level restoration, and its constant ohmic heating for most logic (particularly more than CMOS) which indirectly limits density of components and speed.
Wired logic works by exploiting the high impedance of op...
DTL NAND gate - wired-AND with inverter:
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 RTL and TTL).
The DTL circuit shown in the first picture consists of three stages: an input diode logic stage (D1, D2 and R1), an intermediate level shifting stag...
TTL NAND gate, upgrade on DTL NAND:
To protect them from a short-circuit?
The reason for using wired-AND is because, for RS232 UARTs, the idle state is high, and the active state is low, and only 1 signal goes low at a time, and the diodes isolate the inputs from each other. This is negative-logic, a wired-OR would be used for positive-logic.
I'm using diodes initially, but also bought a few 74HC logic gates last week, just in case.