Recent GP-X boards use a special USB cable for communications. The cable has six wires. You may
want to solder the cable to the top side of the board or the bottom, depending on how you plan to mount
the finished unit. The table below shows where each wire is connected by color:
Color
Function
GP3X connection
Black
Ground
GND (any of the GND pins near the A4 pin on J1)
Red
+5V
+5V (any of the +5V pins near the A4 pin on J1); omit if using seperate power
supply
Yellow
RTS
TTLSER pin 1
Blue
CTS
TTLSER pin 2
White
TX
TTLSER pin 3
Green
RX
TTLSER pin 4
After testing the GP3-X, you may want to use a small zip tie to strain relief the cable by passing the zip
tie through the two large holes in the unused J3 footprint, ensuring that the USB cable is encircled by the
zip tie. Pull the tie tight to lock the cable down to the board.
Older GP3-X boards used a daughterboard for USB communications. The IC4 socket can accept this
USB daughter board (part number UB232R). Normally this board is fitted under the board using the
socket strips supplied with the daughter board. The pins are soldered on the top side of the board (the
side of the board with the silk screen markings). Because of the unusual pin spacing of the daughter
board, one row of pins goes into IC4's pins 1-4. The other row goes into the row of holes marked IC4B
that are nearest to IC4. The USB port should face the edge of the board that holds J1.
Note that because the daughter board is installed under the board, the pin numbers are reversed. That is,
pin 1 of the module corresponds to IC4 pin 8 and the module's pin 8 will connect to IC4 pin 1. With the
USB port on the underside of the board, it is usually a good idea to use spacers or bolts in the four
corner mounting holes to form “feet” for the board so it does not rest on the USB interface.
The connections between the daughter board and the rest of the board appear in the table using the IC4
pin numbers and the module pin numbers for reference. If you wish to power the board from its own
power supply or from an external 5V source, do not connect pin 2 of the USB board. However, if you
wish to operate the board from the USB power supply you can connect pin 2 to one of the holes near JP2
5V and omit IC2 and C6. The jumper on the daughter board should be connected between pins
1 and 2 so that the board operates on 5V instead of 3.3V.
IC4 pin #
USB232 Pin #
GP3X connection
8
1
Ground
7
2
+5V (if USB power desired; no connection if using separate power supply)
6
3
TTLSER-2
5
4
TTLSER-1
2
7
TTLSER-3
1
8
TTLSER-4
Note that it is possible to socket IC2 and the USB module so that the board can operate in either mode.
With the power removed, simply install either IC2 or the USB module as desired. To switch the board to
use the other type of communications, remove the power. Then remove either IC2 or the USB module
and install the other unit.
•
Power – There are several options to power the GP3. The only actual requirement is a regulated 5 volt
(5V) supply. Feeding such a regulated voltage into any of the pins on J1 or J2 marked 5V (and ground
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