Open Drain Output Configuration - Philips P89LPC938 User Manual

Philips Semiconductors
The third pull-up is referred to as the 'strong' pull-up. This pull-up is used to speed up
low-to-high transitions on a quasi-bidirectional port pin when the port latch changes from a
logic 0 to a logic 1. When this occurs, the strong pull-up turns on for two CPU clocks
quickly pulling the port pin high.
The quasi-bidirectional port configuration is shown in
Although the P89LPC938 is a 3 V device most of the pins are 5 V-tolerant. If 5 V is applied
to a pin configured in quasi-bidirectional mode, there will be a current flowing from the pin
to V
quasi-bidirectional mode is discouraged.
A quasi-bidirectional port pin has a Schmitt-triggered input that also has a glitch
suppression circuit
(Please refer to the P89LPC938 data sheet, Dynamic characteristics for glitch filter
specifications).
port latch
data
Fig 10. Quasi-bidirectional output.

5.3 Open drain output configuration

The open drain output configuration turns off all pull-ups and only drives the pull-down
transistor of the port pin when the port latch contains a logic 0. To be used as a logic
output, a port configured in this manner must have an external pull-up, typically a resistor
tied to V
The open drain port configuration is shown in
An open drain port pin has a Schmitt-triggered input that also has a glitch suppression
circuit.
Please refer to the P89LPC938 data sheet, Dynamic characteristics for glitch filter
specifications.
User manual
causing extra power consumption. Therefore, applying 5 V to pins configured in
DD
2 CPU
CLOCK DELAY
. The pull-down for this mode is the same as for the quasi-bidirectional mode.
DD
Rev. 03 — 7 June 2005
Figure
V
DD
P P P
very
strong weak
weak
input
data
glitch rejection
Figure 11.
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
UM10119
P89LPC938 User manual
10.
port
pin
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