AK-3232 Usage Guide

This guide shortly explains how to use the AK-3232 Level Converter. Let’s start with the basics:

Why do I need a RS232 Level Converter?

In general, you need a RS232 Level Converter when connecting the UART of a TTL device (for example, the serial port of your microprocessor) to a standard RS232 serial port of, for example, a PC.

This is because the voltage levels of the TTL device and a RS232 device are different: The TTL device “understands” voltage levels that usually go from 0V to VCC (VCC can be 3V, 3.3V, 5V, depending on your microprocessor). On the other side, RS232 devices “understand” voltages in the ranges of max. -25V to 25V (the RS232 standard specifies a maximum voltage of 25 volts: signal levels of ±5 V, ±10 V, ±12 V, and ±15 V can be used too).

What you can see in the picture below is an example of TTL signals (yellow) and RS232 signals (green):

Difference between TTL and RS232 signals

You may notice that another difference is that TTL devices interpret a logic 1 when the voltage is 0V, and a logic 0 when the voltage is at VCC. RS232 logic is different because a positive voltage means a logic 1 and a negative voltage means logic 0.

What the AK-3232 board does is to convert TTL signals into RS232 signals and viceversa.

Why the voltage levels are different?

TLL voltage levels are not immune enough to external noise. Data along TTL lines can only travel short distances. The voltage levels of a RS232 line allows data to travel distances up to about 300m (with good enough cables).

Hardware

Let’s take a look at the hardware:AK-3232

AK-3232

The AK-3232 is based on the ST3232 chip from STmicroelectronics. The board has 8 signal pins: 2 TTL inputs (IN1 and IN2 on TTL SIDE) and 2 TTL outputs (OUT1 and OUT2 on TTL SIDE). These are the pins you will be connecting to your microcontroller (the TTL device). The RS232 SIDE has two inputs (IN1 and IN2) and two output (OUT1 and OUT2). These are the pins you will connect to the RS232 device. VCC has to be connected to the VCC of the TTL side.

A signal connected to the IN1 of the TTL SIDE will be converted and output to the OUT1 of the RS232 SIDE. A signal connected to the IN1 of the RS232 SIDE be converted and output to the OUT1 of the TTL SIDE. The following picture illustrates this concept better:

AK-232 Signal Directions

Characteristics

The AK-3232 board can be powered up from 3V up to 5.5V, on the VCC pin. The voltage applied to the VCC pin will be used to generate the RS232 output +5V and -5V signals. The AK-3232 can receive on the RS232 side up to +-25V (that is the maximum the standard allows).

AK-3232 connection with flow control

The following illustration shows how to connect the AK-3232 board in a flow control configuration. Here we’ll implement the RX, TX, CTS and RTS signals connected to a standard DB9 female connector.

AK-3232 Flow Control configuration

AK-3232 connection to two serial ports

Since the AK-3232 has 4 inputs and 4 outputs, it can be used to drive two serial ports with a single board. The following illustration shows how to connect 2 serial ports of a microcontroller to two DB9 female connectors.

AK-3232 used for 2 serial ports

Additional information

RS232 DB9 connector pin out

9 Pin D-SUB male connector at the computer. Direction is relative to DTE (computer).

Pin Name Direction Description
1 CD Input Carrier Detect
2 RXD Input Receive Data
3 TXD Output Transmit Data
4 DTR Output Data Terminal Ready
5 GND Ground
6 DSR Input Data Set Ready
7 RTS Output Request to Send
8 CTS Input Clear to Send
9 RI Input Ring Indicator

 

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