1.8V RS232 transceiver, Where?

[Dot]

Hi

I built a SIM7100 daughter board and I would like to debug it through RS232 before moving on and mounting it on its motherboard. The problem is that UART I/O voltage levels are rated for 1.8V and I can't find an RS232 transceiver that can receive 1.8V and output 1.8V to meet with module's I/O. I'm working with 6 UART signals: TX, RX, CTS, RTS, DTR, DCD.

I would prefer to get something on a breakout board.

Thanks

[Richard Crowley]

SparkFun Logic Level Converter - Bi-Directional
The SparkFun bi-directional logic level converter is a small device that safely steps down 5V signals to 3.3V AND steps up 3.3V to 5V at the same time. This level converter also works with 2.8V and 1.8V devices.
https://www.sparkfun.com/products/12009

[rob77]

i would rather suggest a level shifter IC which is guaranteed to work with 1.8V. e.g. TXB0108PWR from TI.
it can translate from anything between 1.2V - 3.6V on port A to anything between 1.65 to 5.5V on port B , it's bi-directional and transparent so it's pretty versatile.
the mosfet shifter Richard suggested above is a great & cheap way of doing it, but i wouldn't go as low as 1.8V with that mosfet solution. it's not so reliable with very low voltages (specially for outputs with "weaker" pull down)

[Monkeh]

One of the wide variety of FTDI ICs with 1.8V supplied to the I/O cells.

[st_ashcroft]

MAX218 works in a similar way to a MAX232 but at lower supply voltages.

https://www.maximintegrated.com/en/products/interface/transceivers/MAX218.html

If you really need all 6 lines you'll need 2.

Cheers,
Scott

[matseng]

Do you really mean RS232 or "TTL-Serial"? 

RS232 is using -12V for Idle/bit-high  and +12V for bit-low.   The Serial like you get out from a FTDI chip have the levels inverted, so +5 for Idle/bit-high and 0 for bit-low.

So while a straight levelshifter like the one from Sparkfun would work if converting from Serial, you'd need something else - like the MAX chips that does the inverting as well.

[Dot]

I will need only TX, RX, CTS and RTS signals for debugging. I found a transceiver like the one below, which is based on SP3232 transceiver IC. I looked in the datasheet, but I'm not sure if it can work with 1.8V.



SP3232 Datasheet: http://www.dexsilicium.com/Sipex_SP3232.pdf

[rob77]

considering the very first sentence in the datsheet of SP3232 "True +3.0V to +5.5V RS-232 Transceivers" - i would say it wont


what you need is either of the following 3 options:
- RS232 transceiver capable of working with 1.8V logic
- logic level shifter 1.8V <-> 3.3V (or 5V) followed by a RS232 trasceiver like the sp3232 or max232 or similar
- logic level shifter 1.8V <-> 3.3V (or 5V) followed by a USB serial module (non RS232) e.g. FT232, CP2102..or similar.

for debugging it makes no sense to convert to RS232, the USB serial would be my choice (unless you're using an ancient computer without USB for debugging )

[Dot]

I was thinking of one breakout board to shift from 1.8V to RS232 voltage levels, but in this case, it seems that two breakout boards are the way to go.

PC <-> SP3232 Board ( VCC = 3 V) <-> TXB0104 Board (VCCA = 3V, VCCB = 1.8V) <-> SIM7100 Module

Actually, I have a SIM7100 Evaluation Board and I looked into the schematic to find out that they're using the same setup as above.

If there's anyone else in the know of one breakout board that can do all of this, please submit a link.

Thank you all for your inputs.