Answers.Body: <p>The RCX input port has a pull-up resistor, not a pull-down (so it reads high: 1024 in raw mode). You can see reverse engineered I/O port electronics here: <a href="http://www.brickshelf.com/cgi-bin/gallery.cgi?f=109570" rel="nofollow noreferrer">http://www.brickshelf.com/cgi-bin/gallery.cgi?f=109570</a></p>
  
  <p><a href="https://i.sstatic.net/EaWya.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/EaWya.jpg" alt="RCX sensor circuit"></a></p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-02-13T12:02:59.647Z
Answers.Text: Thank you for the response! Just want to double-check: if I connect a button to the RCX, it would read that it is on when it is off and vice-versa?
Answers.UserDisplayName: dts
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-02-13T12:55:47.790Z
Answers.Text: Depends on how you read it! in raw mode, you would get 0 (or a low value if your switch has some internal resistance as does the RCX touch sensor) with switch pressed, 1024 if released. But if you configure your sensor as a touch sensor, you'll get 0 if released, 1 if pressed.
Answers.UserDisplayName: Philo
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-02-13T09:54:43.957Z
Answers.LastActivityDate: 2017-02-13T15:13:58.853Z
Answers.LastEditDate: 2017-02-13T15:13:58.853Z
Answers.UserDisplayName: Philo
Body: <p>Sorry for the strange question. I was wondering if anyone knew anything about the internals of the RCX mindstorms brick. Specifically, does it have a pull-down resistor (if no sensor is connected, will it read 0)?</p>
  
Tags: <mindstorms><electronics>
Title: Does the Mindstorms RCX Input Ports have a Pull-Down Resistor?
UserDisplayName: dts
ThreadText: # Does the Mindstorms RCX Input Ports have a Pull-Down Resistor?
  
  (Asked by: username_0 on 2017-02-13)
  
  Sorry for the strange question. I was wondering if anyone knew anything about the internals of the RCX mindstorms brick. Specifically, does it have a pull-down resistor (if no sensor is connected, will it read 0)?
  
  **Tags:** mindstorms, electronics
  
  
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  ## 1 answers
  
  ### Answer by username_1 on 2017-02-13. Score: 4
  
  The RCX input port has a pull-up resistor, not a pull-down (so it reads high: 1024 in raw mode). You can see reverse engineered I/O port electronics here: <http://www.brickshelf.com/cgi-bin/gallery.cgi?f=109570>
  
  [![RCX sensor circuit](https://i.sstatic.net/EaWya.jpg)](https://i.sstatic.net/EaWya.jpg)
  
  > **Comments:**
  > **username_0**: Thank you for the response! Just want to double-check: if I connect a button to the RCX, it would read that it is on when it is off and vice-versa?  
  > **username_1**: Depends on how you read it! in raw mode, you would get 0 (or a low value if your switch has some internal resistance as does the RCX touch sensor) with switch pressed, 1024 if released. But if you configure your sensor as a touch sensor, you'll get 0 if released, 1 if pressed.  
  
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