LPCXpresso Base Board rev B - User’s Guide
Page 54
Copyright 2011 © Embedded Artists AB
6.2
LPCXpresso LPC11C24
The LPC11C24 has fewer available GPIO pins since the on-chip CAN transceiver requires some pins.
There is an Excel sheet that can be downloaded with the pinning of all LPCXpresso modules. This
together with the table in the beginning of chapter 5 gives the differences (compared to the
LPCXpresso LPC1114 Board) that must be considered when using the LPCXpresso LPC11C24
Board:
Pin 42: Is P1.9 on LPC1114 but P3.3 on LPC11C24. This affects control of the red LED in the
RGB-LED.
Pin 46: Is P2.4 on LPC1114 but P2.6 on LPC11C24. This affects how to detect the joystick
down key.
Pin 47: Is P2.5 on LPC1114 but not connected on LPC11C24. This has affect in the irq signal
on the base board.
Pin 48: Is P2.6 on LPC1114 but not connected on LPC11C24.
Pin 51: Is P2.9 on LPC1114 but not connected on LPC11C24.
Pin 53: Is P3.3 on LPC1114 but not connected on LPC11C24. P3.3 is connected to pin 42.
6.3
LPCXpresso LPC176x
6.3.1
GPIO_21/22 needs pull-up resistors
The LPC176x cannot control the signals GPIO_21 and GPIO_22 since these signals connect to P0.27
and P0.28 respectively. These are open drain pins and need pull-up resistors to be able to output a
high signal level. This means that it is impossible to adjust the LPC4811 volume (since the
GPIO_21/22 pins will be constantly low). In order for this to work, simply add pull-up resistors to each
of these pins. 5K-10K ohm is a suitable value on the resistors.
6.3.2
ISP mode UART availability
When setting the LPC176x in ISP mode, J62 shall not be in the default position. See section 4.6.1 for
details about setting.
Note however that even though it is possible to set the LPC176x in ISP
mode it is not possible to download a program image without an external adapter (not included)
that connects to UART#0.
6.3.3
Analog input filtering
It is recommended to add filtering capacitors on the analog inputs, in the 100nF to 1uF range. The
LPCXpresso target boards are build on 2-layer pcb:s and from a noise and grounding perspective, the
layout is not optimal. Adding filtering capacitors (and low-pass filters in general) on the analog signals
will improve accuracy and reduce noise in the ADC conversion.
