All CMOS chips (like the processor on all TS-xxx) have small diodes on all
inputs that clamp the voltage on that input so that the voltage cannot go
much above the positive rail of under the negative rail (usually ground).
These diodes are not discrete parts that are installed on purpose, they are
a result of the CMOS fabrication process. These junctions are very small
and have very limited current capacity, so if you connect an input of such
a chip to a stiff source that is higher than the chip's supply voltage, the
diode will blow, usually causing other damage inside the chip. However, if
you drive for instance an input of a 3.3V powered chip from another chip
that may be 5V powered through a resistor of 1 to a few kOhm, the resistor
will limit the current to a safe value.
I do that routinely. It is particularly effective when the signal is
relatively slow (like the serial data from a GPS receiver) because the
resistor has the side effect of slowing the edges of the signal, and you
could not properly transfer data a 1Mbit/s that way, but for 4800 or 9600
bauds, it is fine.
Didier
On Fri, Feb 28, 2014 at 2:21 PM, Jonathan Leslie <>wrote:
>
>
> wait a sec, the resistor will fix the the 5v to 3.3 volt issue by limiting
> the current? I don't understand.
>
> ------------------------------
> *From:* Didier Juges <>
> *To:*
> *Sent:* Friday, February 28, 2014 3:08 PM
> *Subject:* Re: [ts-7000] TTL serial on a TS7200
>
>
> Be careful that some GPS modules output 5V TTL. That will fry rour
> TS-xxxx in a hurry. I know that for a fact.
>
> You do not need RS-232 level shifters, but you may need one to go from 5V
> to 3.3V. Usually, a 4.7k resistor in series with the Tx output of the GPS
> is all you need. The input of the TS-xxxx will clamp at 3.3V and the
> resistor will limit the current to a safe value. No need to do anything
> with the Tx output of the TS-xxxx. The 5V device will accept 3.3V inputs
> just fine.
>
> Didier
>
>
> On Fri, Feb 28, 2014 at 9:46 AM, Jonathan Leslie <>wrote:
>
>
> I dont' know the ts7200 specifically, but the ts7500 you just solder
> onto the RX and GND pins to the gps modules TX and GND pins and you are
> hardware ready to go. The GPS module broadcasts 1 a second a dump at 4800
> BPS.
>
>
>
>
>
>
> ------------------------------
> *From:* Yan Seiner <>
> *To:*
> *Sent:* Friday, February 28, 2014 10:40 AM
> *Subject:* [ts-7000] TTL serial on a TS7200
>
>
> I have a TS7200 that I'd like to interface with a GPS module. Most of
> the bare modules are TTL - 3.3 to 5V. Is there a way to set up a serial
> port on the 7200 with ttl levels?
>
> I need RX, TX, and DCD pins active on the serial port for the GPS.
>
>
>
>
>
>
>
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