UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 19 December 2013 107 of 841
NXP Semiconductors
UM10360
Chapter 8: LPC176x/5x Pin connect block
The PINMODE_OD registers control the open drain mode for ports. The open drain mode
causes the pin to be pulled low normally if it is configured as an output and the data value
is 0. If the data value is 1, the output drive of the pin is turned off, equivalent to changing
the pin direction. This combination simulates an open drain output.
Function of PINMODE in open drain mode
Normally the value of PINMODE applies to a pin only when it is in the input mode. When a
pin is in the open drain mode, caused by a 1 in the corresponding bit of one of the
PINMODE_OD registers, the input mode still does not apply when the pin is outputting a
0. However, when the pin value is 1, PINMODE applies since this state turns off the pin’s
output driver. For example, this allows for the possibility of configuring a pin to be open
drain with an on-chip pullup. A pullup in this case which is only on when the pin is not
being pulled low by the pin’s own output.
Table 77. Open Drain Pin Mode Select register Bits
PINMODE_OD0 to
PINMODE_OD4
Values
Function Value after
Reset
0 Pin is in the normal (not open drain) mode. 00
1 Pin is in the open drain mode.
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