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Question: RS232 signal level
Posted by: tak ()
Date: May 21, 2015 03:27AM

Am about to start a project that needs to read/write 24C01 EEPROM, but,
got a simple question on the schematic of RS232 interface.
ref: http://www.lancos.com/siprogsch.html#baseboard

The pin8, CTS, looks to be an input to RSR232 from data signal of 24Cxx for
I^2CBus. To my understanding, RS232 requires lower than minus 3 volts for low
level.
The schematic indicates low signal level cannot go lower than zero.

Am I right?
Tak

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Re: Question: RS232 signal level
Posted by: sonix ()
Date: May 21, 2015 07:45PM

Hi Tak,

you are partially right. Yes, the RS232 communication standard use voltage levels +3V ... +15V for data transmission for logical 0 and voltage levels -3V ... -15V for logical 1. This is correct, as you wrote, but it is used only for data transmission (Rx and Tx). The other signals, in this case "handshaking line" CTS (pin 8 at DB9 serial connector) uses standard TTL logic voltage levels 0V and 5V.

Ponyprog's Siprog HW interface uses Tx and partially DTR and RTS lines for feeding power from PC serial port to the serial device which we are trying to communicate with. Data output (from PC to a serial device) is realized through Tx, RTS, DTR lines and as a data input (from a serial device to PC) is used only CTS line.

I hope that this clarifies a little bit the "functionality" of Siprog HW interface.



Yours sincerely
sonix

P.S.:Good luck with your project.

tak Wrote:
-------------------------------------------------------
> Am about to start a project that needs to
> read/write 24C01 EEPROM, but,
> got a simple question on the schematic of RS232
> interface.
> ref:
> http://www.lancos.com/siprogsch.html#baseboard
>
> The pin8, CTS, looks to be an input to RSR232 from
> data signal of 24Cxx for
> I^2CBus. To my understanding, RS232 requires lower
> than minus 3 volts for low
> level.
> The schematic indicates low signal level cannot go
> lower than zero.
>
> Am I right?
> Tak

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Re: Question: RS232 signal level
Posted by: tak ()
Date: May 23, 2015 12:44AM

Thanks, sonix.
I did not know that the CTS uses TTL level. Will re-read the V.28.
Tak



Edited 1 time(s). Last edit at 05/23/2015 12:46AM by tak.

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