[OZAPRS] Small GPS

[Andrew Rich]

I think from memory RS232 is zero is negative volts ?

And a positive in RS232 is above x volts

That is how GARMIN get away with the TTL

- Andrew -


----- Original Message ----- 
From: "Andrew Rich" <vk4tec at tech-software.net>
To: "Australian APRS Users" <ozaprs at aprs.net.au>
Sent: Monday, January 10, 2011 10:26 AM
Subject: Re: [OZAPRS] Small GPS


> The reason I ask is there is TTL and there is TTL
>
> My Garmin GPS 18 5Hz puts out TTL instead of RS323.
>
> In that it goes from 5 volts to 0 volts and tricks the RS232 drivers into 
> thinking it is RS232 levels.
>
> Then there is the PIC TTL.
>
> I have to invert the TTL from the GPS 18 to feed into the PIC
>
> The PIC wants a zero to be a high and then swing low.
>
> I see some "uP friendly" GPS around that do this inverted TTL - feed 
> straight into the PIC
>
> Trying to get my component count down.
>
> - Andrew -
>
> ----- Original Message ----- 
> From: "James Cameron" <vk2lqz at wia.org.au>
> To: "Andrew Rich" <vk4tec at tech-software.net>; "Australian APRS Users" 
> <ozaprs at aprs.net.au>
> Sent: Monday, January 10, 2011 10:15 AM
> Subject: Re: [OZAPRS] Small GPS
>
>
>>I would expect a PIC with a USART to be connected directly to a TTL
>> serial port on a GPS, provided the GPS and the PIC operate on similar
>> levels.  That is, a GPS TTL port may actually be a 3.3V limited port, in
>> which case the PIC should be operated from 3.3V as well.  Unless you add
>> level buffering.
>>
>> -- 
>> James Cameron
>> http://quozl.linux.org.au/
>> _______________________________________________
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>
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