PC RS-232 Threshold Control is in normal operation or fail?

  • Thread starter Thread starter An
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A

An

Hello!
From IBM PC/XT harware books,I know that PC's RS-232 port
uses SN75154 as RS-232 to TTL converting chip. The threshold
control pin is connected to VCC in the hardware book.so the
threshold voltage should be -1.1V,see the the figure.But it
seem's that is not the case,the threshold voltage is about
1.4V in modern computers. Who could please tell me how the
hardware about UART of modern computers changed?
----------------
An
 
I tried to measure one of my PC,The result is that Vit- is about 1.52V
and the Vit+ is about 1.68V .
 
You could start here.
http://en.wikipedia.org/wiki/16550_UART

An wrote:

> Hello!
> From IBM PC/XT harware books,I know that PC's RS-232 port
> uses SN75154 as RS-232 to TTL converting chip. The threshold
> control pin is connected to VCC in the hardware book.so the
> threshold voltage should be -1.1V,see the the figure.But it
> seem's that is not the case,the threshold voltage is about
> 1.4V in modern computers. Who could please tell me how the
> hardware about UART of modern computers changed?
> ----------------
> An
>
>
>
 
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