Техническая Спецификация для Embedded Artists LPCXPRESSO BASE BOARD EA-XPR-021 EA-XPR-021

LPCXpresso Base Board rev B - User’s Guide 

Page 56 

 

 

 

Copyright 2013 © Embedded Artists AB 

 

Reason 1: If a terminal application, such as Tera Term, is connected to the COM port associated with 

the board and at the same time have the J54 jumpers (see Figure 21) inserted, the terminal application 

might be the cause of this problem. If the terminal application is pulling DTR low the board will be reset 
and if it pulls RTS low it will control the bootload enable functionality. 
Solution 1: Remove the jumpers and try again (please note that the jumpers must be inserted if the 

board is programmed using the UART boot mode). 
 
Reason 2: If the board is powered only through the USB interface on the LPCXpresso LPC1xxx Board 

(interface 2 as shown in Figure 3) the FTDI USB-to-UART bridge won’t be powered. The output pins 

such as RTS and CTS might then have a low output. If the J54 jumpers, see Figure 21, are inserted 

the board will always be in reset. 
Solution 2: Power the board also through USB interface #1, as shown in Figure 3, or remove the J54 
jumpers.  

The LPCXpresso Base Board shall be powered from a PC via the included USB cable (mini-B to A 

cable). Up to 500mA can be drawn from the USB port. 
Reason: The LPCXpresso Base Board and LPCXpresso LPC1xxx Board do not receive enough 

current. Symptoms when insufficient power is supplied can exhibit itself in a number of ways; the board 
may appear to work, but: 

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you mail fail to program the Flash on the device (as more power is drawn), or 

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the debugger may not be able to find the target, or 

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the debugger may disconnect unexpectedly, or 

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a variety of other inexplicable errors! 

Solution 1: Make sure the main power source is the USB-to-UART bridge. See Figure 3. 
Solution 2: Not all PC USB ports supply the specified top current (500 mA). This is especially true for 

laptops, but affects many desktop PCs too. Use a powered USB hub to power the LPCXpresso Base 

Board. 

The trimming potentiometer (R105) can be used to create an analog voltage to GPIO_11 (analog input 

1). The lowest possible reading can be between 20-40 (on a scale from 0 to 1023) even if the trimming 
potentiometer is turned to the lowest output voltage. 
Reason: There are pull-up resistors on GPIO_11 that will generate a current through R106. One pull-

up resistor is internal in the LPC1xxx and can be disabled via program control. The other pull-up 

resistor is R46 (via R57), found on schematic page 4. These resistors are actually mounted even 

though the schematic indicate that this is an optional mounting. The voltage across R106 can be up to 
about 0.1 volt due to the pull-up resistors on GPIO_11. 
Solution: Make sure that GPIO_11 does not have the (LPC1xxx) internal pull-up resistor enabled. This 

is a pin configuration. Also remove R57 or R46. Either of these resistors can easily be de-soldered 

from the pcb.