Just a few words about the serial connection on the CubieBoard. I have bought my CubieBoard during the indiegogo campaign, and I have bought the Rich Package. This Rich Package also includes a serial cable. This serial cable is an USB to 3.3 Volt UART, which is based upon the pl2303 chip. It has four connectors, Rx, Tx, Ground and 5 Volt.

pl2303 from cubieboard rich package

The red cable is a 5 Volt power supply. Since the I/O lines on the CubieBoard are 3.3 Volt, this should not be connected. Besides, the Vcc pin on the serial connected is a power source, not a power input. So, when using a pl2303, the Vcc should not be connected.

CubieBoard Serial TTL

If you’ve read my previous post, you see the problem I’ve encountered: when there was already a USB serial device inserted, the device got a different device name. /dev/ttyUSB0 /dev/ttyUSB1 etc, depending on the sequence they were plugged in, or, at boot time, the port in which they are plugged. So, for this reason, I would like to use real RS-232 ports in stead of those USB UART devices.

My BeagleBoard got an R-S232 port, so I just plug in a nullmodem cable and that’s it. On the CubieBoard, as mentioned before, the signal levels are 3.3 Volt. A MAX3232 based board can be used to convert the signal levels. I’ve bought such a board at dealextreme. When we use this, we will need to connect the Vcc line.

We connect the Vcc on the CubieBoard to the Vcc on the MAX3232 board, the Ground to the Ground, but the Tx and Rx we have to swap. Tx is transmit and Rx is receive. But what the Cubieboard sends is what the RS232 port on my computer will receive, vice versa.

MAX3232 Board

CubieBoard to MAX3232

The colours you see in these pictures are no standard colours whatsoever. I just have these wires for general purpose. From what I have read on various places on the internet, the connectors are called dupont connectors. I never knew they were called like that. (Actually, I have no clue how an native English speaking person would pronounce that… it *looks* French to me)

Rainbow dupont flatcable

Anyhow, mentioning I/O Voltages, I would like to add, the CubieBoard and Raspberry Pi use 3,3 Volt I/O, but the BeagleBoard uses 1.8 Volt I/O. Keep this in mind when interfacing hardware. Different voltage on the BeagleBoard!


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