Datasheet

NXP Semiconductors
UM11121
LPCXpresso51U68
UM11121
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© NXP Semiconductors N.V. 2018. All rights reserved.
User manual
Rev 1.1 — 27 April 27, 2018
11 of 22
Fig 3. FTDI connector
Table 2. P3 FTDI interface
LPC51U68 Signal
FTDI signal
Pin #
Direction
LPC51U68 Signal
GND
GND
1
GND
No connect
CTS
2
No connect
Board +5V
5V
3
Board +5V
UART0_RXD
TXD
4
From host
UART0_RXD
UART0_TXD
RXD
5
To host
UART0_TXD
No connect
RTS
6
GND
5. Board power connections and measurement
The LPCXpresso51U68 board requires +5V input to power the on-board voltage
regulators which in turn power the Link2 debug probe and other +3.3V circuits, the
LPC51U68 target and other +1.8V circuits, and the Arduino +5V and +3.3V power rails.
When the main external power source is from the Link2 side USB micro B-type connector
(J7), both the Link side and LPC51U68 Target sections of the board are powered. When
the main external power is from the Target side USB micro B-type connector (J5), or
FTDI header (P3) only the LPC51U68 Target section of the board is powered.
A block diagram of the board power tree is shown in Fig 4. When the LPC51U68 Target
is to be debugged from an external debug probe, instead of the on-board Link2 debug
probe, the Link USB connector (J7) must be disconnected. The circle with I indicates
where the current monitoring circuitry measures / where an ammeter can be inserted.
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2
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4
5
6