Subject:
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Re: 6 servos and RS232...
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Wed, 22 May 1996 16:57:02 GMT
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Original-From:
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[ian.blythe@]antispam[st.com]
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Viewed:
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1087 times
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> > > The boards take serial input (2400 or 9600 baud). It is
> > > straightforward to write a 6811 assembly routine to output such serial
> > > signals on an arbitrary digital output.
> > Are the digital outputs at 5v high? I think you mentioned on the HB
> > homepage about the serial interface converting RS232 levels at +12 and
> > -12v to TTL level s (5v). I'm not that familiar with the nitty gritty
> > of RS232 so this kinda puzz les me.
> There are two types of serial voltages: TTL level and RS-232 level.
> The HB's serial interface board converts from TTL to RS-232 for
> communicating with the host computer.
> The Scott Edwards board accepts TTL levels, so an HB pin can drive it
> directly.
> The translation between logical level (e.g., is the bit a 1 or a 0),
> TTL, and RS-232 is anything but obvious:
> logical level TTL level RS-232 level
> zero or idle +5v -12v
> one 0v +12v
From memory of my designer engineer days, the EIA RS232 specification
quotes something along the lines of:
logical level RS-232 level
zero or idle -3V to +15V
one +3V to -15V
The spec gave maximum slew rates for signals and such specifics such as
if a signal level went below +3V or above -3V then the signal level must
fall/rise to the opposite 3V level to give a true signal level change.
The signal levels show why some circuit tricks using 0V, +5V can work,
but not when you connect it to a true RS232 connection.
Those were the days though, RS232 talks about Data Communication Devices
(DCD) and Data Terminal Equipment (DTE), the DCD being the modem, and the
DTE being the terminal VDU, the computer being in a room somewhere else
(no Personal Computing!). This is why there is the cross-over on TxD and
RxD (pins 2 and 3) when you connect a PC and PC (DTE to DTE or is it DCD
to DCD?)!
There is more to this story, but this is not the right place, there must
be a FAQ somewhere!
sorry to be so picky... :)
regards to all
Ian
ian.blythe@st.com
100116.3072@compuserve.com
words are but mine own, I speaketh for none other
- did Shakespeare really speak English?
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Message is in Reply To:
 | | Re: 6 servos
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| (...) There are two types of serial voltages: TTL level and RS-232 level. The HB's serial interface board converts from TTL to RS-232 for communicating with the host computer. The Scott Edwards board accepts TTL levels, so an HB pin can drive it (...) (29 years ago, 22-May-96, to lugnet.robotics.handyboard)
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