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'[PICLIST] [PIC] - 16f628 and PICUSART.ASM'
Can anyone help me out with getting the 16f628 to work with the picusart
What is a MAX232? Do I have to have one to talk to a PC?
I will probably use VB to build the PC interface.
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Byron A Jeff
David P. Harris
Harold M Hallikainen
| And regarding the second question (MAX232), yes, you generally need to
convert from TTL levels to EIA232 levels. The USART outputs a 1 (+5V) for
the mark condition, and outputs 0V for the space condition. EIA232 is
generally -12V for mark (there's actually a wide range of acceptable
voltages, but -12V is typical), and +12V for space. So, you need to
invert the signal and change voltage levels. Most EIA232 receivers will
accept 0V as a mark, so it's possible (though not within the standard) to
directly drive an EIA232 receiver with TTL levels. However, the logic
levels still need to be inverted, since a low (-12V) is a mark. If you
are bit banging the data, you can do this inversion in software. If
you're using the USART, you need to do this change in hardware.
The old standard chips are the MC1488 quad EIA232 driver and the MC1489
EIA232 receiver. Maxim has a variety of EIA232 transmitters, receivers,
and transceivers. An interesting one I used recently is the MAX221. Its
charge pumps shut down if there is not a valid EIA232 voltage on its
receiver input, vastly decreasing power consumption when nothing is
plugged into the EIA232 port. It also has a pin that goes high when a
valid EIA signal is present. I tell the PIC16f870 to sleep when there's
no terminal connected.
On Fri, 31 May 2002 09:44:08 +1000 Tony Nixon
<ENG.MONASH.EDU.AU> writes: Tony.Nixon
FCC Rules Online at http://hallikainen.com/FccRules
Lighting control for theatre and television at http://www.dovesystems.com
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