TLL port arduino pro mini communication

Hello! I want to make serial communication between E-reader Kobo and Arduino pro mini. The reader has a TTL port on the board. I want to ask if I can connect the TTL serial port to any digital pin on Arduino and use the SoftwareSerial library or do I have to use the RX0 TX0 pins and use the serial library?

Are those 5V signals ? I suggest to use 1k in the signal path to protect both the Arduino and the Kobo.

The Pro Mini has a ATmega328P chip, which is the same as in the Arduino Uno. So yes, you can use any pin, since any pin can be a "Pin Change Interrupt" (PCINT) with that chip, and the PCINT is used by the SoftwareSerial library.

SoftwareSerial can't handle high speeds (115200 baud) and it can't receive at the same time it's transmitting. Unless you already need to use TX0 and RX0 to communicate with something else, I would suggest you connect them to the Kobo and don't use SoftwareSerial.

There are two flavors of Pro-Mini (3.3V & 5V). You didn't tell us which one you have.

Are those 5V signals ? I suggest to use 1k in the signal path to protect both the Arduino and the Kobo.

TTL means 5V signals. (last time I checked) Is there another TTL I am not aware of ?

TTL doesn't mean 5v. A 3.3v Arduino Due has TTL input and output.

He's got you there Rasch!

Whilst TTL logic runs on 5V, the levels actually correspond to 3.3V CMOS logic.

That is after all why they had to make "HCT" series CMOS.

DOOH ! :-[

According to THIS you're both wrong. It clearly shows "TTL" voltage levels as 0 - 5V, and CMOS levels as (what you said). (that's why I asked if there was another TTL I was not aware of) . It is also the reason for the existance of the TTL-CMOS/CMOS-TTL logic level converter chip CD4050 or 74HC4050. When you purchase a TTL VFD (Vacuum Fluorescent Display (like you see on most cash registers at McDonald's and other fast food restaurants), the datasheet or vendor websites states it runs on serial 0 to 5V TTL signals.

raschemmel: According to THIS you're both wrong. It clearly shows "TTL" voltage levels as 0 - 5V, and CMOS levels as (what you said).

Err, no it actually doesn't say any such thing!

For example, TTL levels are different from those of CMOS. Generally a TTL output does not rise high enough to be reliably recognised as a logic 1 by a CMOS input, especially if it is only connected to a high-input-impedance CMOS input that does not source significant current.

A TTL "HIGH" according to the table in the section I first linked, is 2V or over. In 5V CMOS, 2V is a LOW.

Your not making sense. I said they are different levels and that's why you need the level converter chip. You replied back that they are different levels (in your own words). We are saying the same thing. TTL is NOT CMOS. I started out saying that the OP claimed his device uses TTL.

The reader has a TTL port on the board

I said there is only one and it is 0-5V . You are implying there is a TTL-TTL and a CMOS-TTL. My original assertion is there is only one TTL and if the OP is citing that , it means 0-5V , because that is what TTL is. He didn't say it was CMOS.

this:

TTL doesn't mean 5v. A 3.3v Arduino Due has TTL input and output.

is based on this:

The SAM3X provides one hardware UART and three hardware USARTs for TTL (3.3V) serial communication.

(from Arduino product site)

I think it is a misuse of the term "TTL" intended to imply 3.3V CMOS logic levels. I don't know if that is the case so I really can't defend my position without verifying that.

I have never heard of 3.3V TTL. 3.3V to me means CMOS logic levels.

I need someone to post a link to a reference webpage that shows the logic levels for 3.3V TTL, (if it exists) alongside the 3.3V CMOS logic levels showing they are different. If I saw that then I would concede there is MORE than ONE TTL . (recall my question about that ?)

Classic forum discussion - OP asks a question, and then we have 3+days of tangential discussion and never hear from the OP again.

@raschemmel, try this link http://www.interfacebus.com/voltage_threshold.html has a nice picture of the different levels for the different families.

@Crossroads, Thanks for the link. Too bad it doesn't work . What happened to Interfacebus.com ?

@polachp, you may want to look at this video I made some time ago…

I found this , which I believe refers to a standard called LVTTL which is NOT what the OP said his device uses.

Hmm, okay, try this one then http://dangerousprototypes.com/2011/04/25/voltage-threshold-chart/

From the link Crossroads just posted:

Many 5volt chips will working with the output from a 3.3volt part. An example is the Arduino, it sees 3volts or more as a ‘1’. A 3.3volt device with 5volt tolerant pins, such as the Bus Pirate, can interact with an Arduino despite the voltage difference.

This table shows common logic threshold voltage levels and where they’re compatible.

The graph provides a comparison of Input and Output [I/O] logic switching levels for the CMOS, TTL, mixed CMOS/TTL, ETL, BTL, GTL, and Low voltage glue logic families. The graph above provides a comparison between the Input and Output [I/O] logic switching levels for CMOS, and TTL logic families.

The graph shows 5 volt CMOS, TTL, and mixed CMOS/TTL IC devices, and 3.3 volt LVTTL LVCMOS IC devices. BTL and GTL [Bus Driver] IC are shown for comparison. Note many Low Voltage [LV] CMOS families are 5 volt tolerant [not damaged by applying 5v to the input pins]. The output logic levels above are defined by the Terms section below. For a review of Noise Margin numbers and a short description of many of the IC logic families, refer to the Logic Family Selection page.

My question from Reply#3:

TTL means 5V signals. (last time I checked) Is there another TTL I am not aware of ?

It would appear there is a subset of TTL known as LVTTL which is NOT what the OP stated his device uses. however, as stated above:

Many 5volt chips will working with the output from a 3.3volt part.

Many times when the term TTL is thrown about, the speaker really means "logic level." Back when TTL was the dominant logic family, the terms were interchangeable. But now that there are so many logic families and operating voltages, TTL is hardly the most common and "logic level" really has no precise meaning.

When used in relation to a serial connection, "TTL" is often (incorrectly) used to mean "logic level" as opposed to higher +/- voltage RS-232 levels. Whenever I see the term, I assume it means negative logic and low voltage logic levels, but I make no assumptions about the actual voltage levels. Always read the data sheet.

This thread is going down a rat hole arguing over the thresholds of various device families, all because the TTL term was taken literally. The only real answer is to ignore the term which could have been used erroneously, and just look at the specifications of the device. If the device's specs aren't detailed enough, look at the chip that is the actual interface and check it's data sheet. It's the only way to know for sure.

This thread is going down a rat hole arguing over the thresholds of various device families, all because the TTL term was taken literally. The only real answer is to ignore the term which could have been used erroneously, and just look at the specifications of the device. If the device's specs aren't detailed enough, look at the chip that is the actual interface and check it's data sheet. It's the only way to know for sure.

That's funny because the SPECs for the KOBOs don't mention TTL at all. It lists USB or mini USB or Micro USB, but ABSOLUTELY NOTHING ABOUT TTL.

As everyone knows USB is RS-485 differential drive. The voltage levels may be 5V but I would hardly call USB TTL, simply because it is not compatible with TTL chips , which is in fact the entire reason you need the onboard FTDI chip or a standalone FTDI if interfacing with a Pro-Mini or ATmega328 chip.

So once again , we have been given bad Intell.

@OP, Please explain why you stated the KOBO uses TTL. Cite your reference links.

Thanks for bringing that up Shapeshifter.

I understand my previous comment here went unnoticed... the Kobo has an internal serial connection (RX/TX), it's not exposed to the end user but can be reached if one disregards warranty and opens the case.

It transmits the output of its linux-ish OS at 115,200 baud, if I remember correctly, and can be read using a simple USB-to-UART adapter (5V). SoftwareSerial is not capable of receiving this. When I played with this connection, about a year and a half ago, I couldn't find a way to get a response from the device, but that doesn't prove anything :)

if I remember correctly, and can be read using a simple USB-to-UART adapter (5V).

It would have been nice if you had mentioned this when you mentioned the TTL port on the board (which I couldn't find any indication of in the specs)

USB-to-UART

is FTDI (USB to TTL). FTDI

When I played with this connection, about a year and a half ago, I couldn't find a way to get a response from the device, but that doesn't prove anything :)

How exactly did you try to do that ?

raschemmel: It would have been nice if you had mentioned this when you mentioned the TTL port on the board (which I couldn't find any indication of in the specs)

...are you referring to me or to the OP?

raschemmel: is FTDI (USB to TTL). FTDI

FTDI is a specific manufacturer, there are plenty others - I used a $2 no-brand module from china :)

raschemmel: How exactly did you try to do that ?

Sent all sorts of characters and strings... nothing seemed to have any effect. But again, I might have missed something obvious.