BS2px -vs- other stamps questions
HomeSchoolDad
Posts: 32
Greetings again,
Since I decided to use external memory I have been looking at moving my project to the BS2px for the extra speed, but as a beginner I am having trouble understanding the implications that the extra features in this stamp module actually impose or how those features translate to wiring differences between this module and the BS2pe that I am currently using.
Please excuse yet another list of questions:
1.) When I am using I2C with by BS2pe I have to use pull-up resistors. Since the BS2px has a "built-in, user-configurable Pull-up Resistor...on every I/O pin" does that mean I no longer need to have those and should ignore the I2COUT special notes that say that the pull-up resistors are required?
2.) Does the use of the 16 bit I/O expander MCP23016 complicate matters when I wire up buttons on it -vs- wiring for direct connect to the BS2px with its new features? How should the buttons be wired and features be set up if they are different on this stamp vs the other BS2 stamps?
3.) I use a 3 volt DataFlash in the design with a pull-up on the SO port. I assume I no longer would need that? I notice that the specs say the pull-up is 20 ohm and I use 4.7 resistors from a suggestion by Jon. What does that difference mean exactly and do I need to even pay attention to that difference?
4.) The spec also says there is a voltage comparitor. Can I use that to monitor battery voltage levels in some way?
5.) While I have a minimal intellectual understanding of the Schmitt Triggers and Logic Thresholds that come on the BS2px, I don't have the practical feel for them that can only come from experience. It appears to me that Schmitt Triggers and Logic Threshold CMOS and TTL settings are all mutually exclusive. Is this true or is there an instance where I need to combine them for a desired effect?
I know that is a long list of questions, but I just can't stop myself from asking. I hope that they are appropriate to include in a single thread as titled in the subject. let me know if I should break some/all of them out to separate threads. Thanks again, anyone, for any answers you can give me.
Jeff Brower
Since I decided to use external memory I have been looking at moving my project to the BS2px for the extra speed, but as a beginner I am having trouble understanding the implications that the extra features in this stamp module actually impose or how those features translate to wiring differences between this module and the BS2pe that I am currently using.
Please excuse yet another list of questions:
1.) When I am using I2C with by BS2pe I have to use pull-up resistors. Since the BS2px has a "built-in, user-configurable Pull-up Resistor...on every I/O pin" does that mean I no longer need to have those and should ignore the I2COUT special notes that say that the pull-up resistors are required?
2.) Does the use of the 16 bit I/O expander MCP23016 complicate matters when I wire up buttons on it -vs- wiring for direct connect to the BS2px with its new features? How should the buttons be wired and features be set up if they are different on this stamp vs the other BS2 stamps?
3.) I use a 3 volt DataFlash in the design with a pull-up on the SO port. I assume I no longer would need that? I notice that the specs say the pull-up is 20 ohm and I use 4.7 resistors from a suggestion by Jon. What does that difference mean exactly and do I need to even pay attention to that difference?
4.) The spec also says there is a voltage comparitor. Can I use that to monitor battery voltage levels in some way?
5.) While I have a minimal intellectual understanding of the Schmitt Triggers and Logic Thresholds that come on the BS2px, I don't have the practical feel for them that can only come from experience. It appears to me that Schmitt Triggers and Logic Threshold CMOS and TTL settings are all mutually exclusive. Is this true or is there an instance where I need to combine them for a desired effect?
I know that is a long list of questions, but I just can't stop myself from asking. I hope that they are appropriate to include in a single thread as titled in the subject. let me know if I should break some/all of them out to separate threads. Thanks again, anyone, for any answers you can give me.
Jeff Brower
Comments
1) While the BS2px has internal pull-up resistors, these are defined as "weak" pull-ups and usually used to keep the lines from oscillating· when not connecting, or when using the pins as inputs.· Typically·I2C·uses 4.7K resistors, so I would probably stick with those.
2) I'm a little confused on what you're asking here.· Why should switches be wired any differently depending on which Stamp Model the expander is connected to?
3) Again, this pertains to question #1, and is certainly dependant on the device and what else might be sharing the lines, as is often the case with I2C devices.
4) This was recently discussed in the forums.· Definately do a quick search and see what you can find.
5) The example for CONFIGPIN in the help file explains this, and in fact you can specify multiple options for given pins based on the mask you specify for each more.· Again, check the help file example.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
2) The MCP23016 is general-purpose -- you can wire buttons any way you'd like. The chip does allow you to invert inputs so you can make active-low inputs look active-high.
4) Yes; you can use another pin with PWM to create an output and with a bit of code have an eight-bit ADC (input is limited to 5 volts).
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Jon Williams
Applications Engineer, Parallax