DEC bus transceivers

Paul Koning paulkoning at
Mon Oct 24 11:01:50 CDT 2016

> On Oct 23, 2016, at 2:50 PM, shadoooo <shadoooo at> wrote:
> ...
> The idea of using bare transistors seems to me too much simple.
> Not that it couldn't work, but it would be almost impossible to satisfy all
> the specifications of the bus in this way... unless you use a more complex
> circuit with precise current sources and resistors to grant correct voltage
> biases, impedances and slew rates, which in the end is a logic integrated
> circuit.

I don't know about the receiver part, but I'd expect that the drivers could very easily be done with a simple transistor circuit.  After all, that's what an open collector (or open drain) driver is, in essence.  And the spec is quite straightforward, it demands an adequate current sinking capacity which is easy to meet.  As for slew rates, unless you have antique transistors, that's not going to be an issue given that you meet the current sink spec; the slew rate of an OC circuit is determined by the system capacitance and the sink current of the driver.

Some fiddling with SPICE should yield simple answers here.


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