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Discussion Groups | LPC900 | Problem using LPC952 port 5 (P5.x) as open drain outputs
Find help, specifications and source code for the LPC900. The LPC900 challenges Microchip and AVR based on the worlds most popular 8-bit architecture the 80C51. With a 2-clock core the LPC900 series is a high performance, very flexible and low cost 8-bit microcontroller family. Designers using or interested in these devices are encouraged to share their know-how and ask questions.
Problem using LPC952 port 5 (P5.x) as open drain outputs - fabiosomenzi - May 30 2:54:31 2008
Hello,
I tried to configure all P5.x pins as open drain outputs, setting both
P5M1 and P5M2 to 0xFFH. My target application has this kind of circuit
attached to each P5.x pin: a resistor to the base of a PNP transistor,
which emitter is tied to +5V. I set all P5 pins to logic "1" on the
program initialization. But instead of being open after program starts,
the transistors conduct since there is a current flowing through the
base resistors to the P5.x pins. It's like some sort of LPC952 internal
pull-up is not being disabled, but should be in open-drain port mode.
I must say that the same circuit attached to P4.x pins works properly.
That is, the problem only happens with P5 port.
Any help?
Thanks,
Fabio Somenzi
------------------------------------
(You need to be a member of LPC900_users -- send a blank email to LPC900_users-subscribe@yahoogroups.com )
I tried to configure all P5.x pins as open drain outputs, setting both
P5M1 and P5M2 to 0xFFH. My target application has this kind of circuit
attached to each P5.x pin: a resistor to the base of a PNP transistor,
which emitter is tied to +5V. I set all P5 pins to logic "1" on the
program initialization. But instead of being open after program starts,
the transistors conduct since there is a current flowing through the
base resistors to the P5.x pins. It's like some sort of LPC952 internal
pull-up is not being disabled, but should be in open-drain port mode.
I must say that the same circuit attached to P4.x pins works properly.
That is, the problem only happens with P5 port.
Any help?
Thanks,
Fabio Somenzi
------------------------------------
(You need to be a member of LPC900_users -- send a blank email to LPC900_users-subscribe@yahoogroups.com )
Re: Problem using LPC952 port 5 (P5.x) as open drain outputs - Willard - May 30 9:09:50 2008
In any case you probably should add a pullup to 5v to handle any leakage that will occur.
You can calculate how much leakage you have by measuring the voltage drop across the base
resistor.
WT
----- Original Message -----
From: fabiosomenzi
To: l...@yahoogroups.com
Sent: Friday, May 30, 2008 1:54 AM
Subject: [lpc900_users] Problem using LPC952 port 5 (P5.x) as open drain outputs
Hello,
I tried to configure all P5.x pins as open drain outputs, setting both
P5M1 and P5M2 to 0xFFH. My target application has this kind of circuit
attached to each P5.x pin: a resistor to the base of a PNP transistor,
which emitter is tied to +5V. I set all P5 pins to logic "1" on the
program initialization. But instead of being open after program starts,
the transistors conduct since there is a current flowing through the
base resistors to the P5.x pins. It's like some sort of LPC952 internal
pull-up is not being disabled, but should be in open-drain port mode.
I must say that the same circuit attached to P4.x pins works properly.
That is, the problem only happens with P5 port.
Any help?
Thanks,
Fabio Somenzi
(You need to be a member of LPC900_users -- send a blank email to LPC900_users-subscribe@yahoogroups.com )
WT
----- Original Message -----
From: fabiosomenzi
To: l...@yahoogroups.com
Sent: Friday, May 30, 2008 1:54 AM
Subject: [lpc900_users] Problem using LPC952 port 5 (P5.x) as open drain outputs
Hello,
I tried to configure all P5.x pins as open drain outputs, setting both
P5M1 and P5M2 to 0xFFH. My target application has this kind of circuit
attached to each P5.x pin: a resistor to the base of a PNP transistor,
which emitter is tied to +5V. I set all P5 pins to logic "1" on the
program initialization. But instead of being open after program starts,
the transistors conduct since there is a current flowing through the
base resistors to the P5.x pins. It's like some sort of LPC952 internal
pull-up is not being disabled, but should be in open-drain port mode.
I must say that the same circuit attached to P4.x pins works properly.
That is, the problem only happens with P5 port.
Any help?
Thanks,
Fabio Somenzi
(You need to be a member of LPC900_users -- send a blank email to LPC900_users-subscribe@yahoogroups.com )