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What for are these connectors on (older) Arduinos? Answered

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On Arduino Duemilanove and some other boards (but not on Arduino Uno) there are four small plates near usb socket, numbered 4 3 2 1. On official photos they are just plates, but on my Hong Kong board there are male header pins instead. They are not mentioned in general texts about the board and I can't seem to know the right phrase to successfulli google it.

What are these four connections for?

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frollardBest Answer (author)2011-12-06

http://arduino.cc/en/Main/ArduinoBoardDuemilanove

There are links for schematics there;

http://arduino.cc/en/uploads/Main/arduino-duemilanove-schematic.pdf

Which shows those pads coming directly off the FTDI serial chip, header X3.
1CTS
2DSR
3DTD
4RI

From the ftdi datasheet:

"Pin No. Name Type Description
1
TXD
Output
Transmit Asynchronous Data Output.
2
DTR#
Output
Data Terminal Ready Control Output / Handshake Signal.
3
RTS#
Output
Request to Send Control Output / Handshake Signal.
5
RXD
Input
Receiving Asynchronous Data Input.
6
RI#
Input
Ring Indicator Control Input. When remote wake up is enabled in the internal EEPROM taking RI# low (20ms active low pulse) can be used to resume the PC USB host controller from suspend.
9
DSR#
Input
Data Set Ready Control Input / Handshake Signal.
10
DCD#
Input
Data Carrier Detect Control Input.
11
CTS#
Input
Clear To Send Control Input / Handshake Signal.
12
CBUS4
I/O
Configurable CBUS output only Pin. Function of this pin is configured in the device internal EEPROM. Factory default configuration is SLEEP#. See CBUS Signal Options, Table 3.9.
13
CBUS2
I/O
Configurable CBUS I/O Pin. Function of this pin is configured in the device internal EEPROM. Factory default configuration is TXDEN. See CBUS Signal Options, Table 3.9."

Basically, functions on the ftdi chip that 99% of people will never need/use. Since the new duinos don't use the chip, they don't get included on newer boards.

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