Author Topic: Why two inputs?  (Read 828 times)

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Offline viperidae

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Why two inputs?
« on: February 07, 2019, 07:26:52 am »
Looking at the datasheet for this bus interface IC, there are two inputs. They're both identical. Why would they do that?
https://www.renesas.com/us/en/doc/products/assp/rej03f0095_ha12240fp.pdf
S1 and S2 are both TX inputs.
 

Offline vealmike

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Re: Why two inputs?
« Reply #1 on: February 07, 2019, 07:45:39 am »
Looking at the datasheet for this bus interface IC, there are two inputs. They're both identical. Why would they do that?
https://www.renesas.com/us/en/doc/products/assp/rej03f0095_ha12240fp.pdf
S1 and S2 are both TX inputs.
Philosophical rather than electrical your question is. The application must you consider. To see a wood, one must first ignore the trees. Change must come from within, but charge a product of time and current it is.
Yeerrs.
 
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Offline viperidae

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Re: Why two inputs?
« Reply #2 on: February 07, 2019, 08:01:51 am »
The application for the chip is a physical driver for IEBus, to connect to a NEC/Renesas MCU with a built in IEBus controller.
Those built in controllers only have one TX output.
 

Online Ice-Tea

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Re: Why two inputs?
« Reply #3 on: February 07, 2019, 08:07:04 am »
S1 and S2 are followed by an OR gate. So it allows some sort of multiplexing or logic gating. If you don't need it, tie it to ground.

Offline bsudbrink

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Re: Why two inputs?
« Reply #4 on: February 07, 2019, 05:20:11 pm »
Looking at the datasheet for this bus interface IC, there are two inputs. They're both identical. Why would they do that?
https://www.renesas.com/us/en/doc/products/assp/rej03f0095_ha12240fp.pdf
S1 and S2 are both TX inputs.
Philosophical rather than electrical your question is. The application must you consider. To see a wood, one must first ignore the trees. Change must come from within, but charge a product of time and current it is.
Yeerrs.

Stock in Disney/Lucas Arts he owns.
 

Offline David Hess

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Re: Why two inputs?
« Reply #5 on: February 07, 2019, 07:07:33 pm »
The second input allows the output to be set into a known state without relying on the data source.  This can be especially important when the data source uses a different power domain and may generate spurious data during power up or power down.  The ancient 1488 RS-232 line driver and many other interface ICs have dual inputs also for the same reason.
 

Offline viperidae

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Re: Why two inputs?
« Reply #6 on: February 07, 2019, 09:36:41 pm »
S1 and S2 are followed by an OR gate. So it allows some sort of multiplexing or logic gating. If you don't need it, tie it to ground.
According to the equivalent circuit, these are "active low" inputs, driving the base of a PNP transistor. I think I'll need to tie them together or tie one high.
 

Online Ice-Tea

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Re: Why two inputs?
« Reply #7 on: February 08, 2019, 06:43:24 am »
S1 and S2 are followed by an OR gate. So it allows some sort of multiplexing or logic gating. If you don't need it, tie it to ground.
According to the equivalent circuit, these are "active low" inputs, driving the base of a PNP transistor. I think I'll need to tie them together or tie one high.

The DS clearly states that logic high is 2.1V or above.


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