Programmable pull-up resistor in Cyclone II

[Altera_Forum]

Dear Sir, 

 I've a question about the pull-up resistor. Suppose, the pull-up resistor is related to the I/O voltage Vccio and current strength, isn't it? Why does it show the resistor is about 10KOhm to 50KOhm in the table5-3 of Cyclone II Device handbook chapter 5? For example, Vccio=3.3V, Current strength 16mA in Default of LVTTL. The pull-up is supposed to be around Rpull-up = (3.3/16)KOhm, isn't it?   Regards,     Peter Chang

[Altera_Forum]

--- Quote Start ---  Suppose, the pull-up resistor is related to the I/O voltage Vccio and current strength.  --- Quote End ---   It isn't. The value is fixed, but subject to PVT (process, voltage, temperature) variations.

[Altera_Forum]

Dear Sir, 

 But I could see a similar example from the page of 8-3 to 8-5 in the MAXII Device Handbook, max2_mii5v1.pdf. It is for the REXT. It, however, is able to be used for an internal resistor, RINT, isn't it?   Regards,   Peter Chang:confused:

[Altera_Forum]

In the device handbook, the minimum value for an external pull-up resistor is calculated. The internal pull-up resistor is in contrast a weak pull-up with a resistance several orders of magnitude above this minimum value.

[Altera_Forum]

Dear FvM, 

 Why do we need both? Suppose, we need only either internal or external resistor, needn't we?     Peter Chang

[Altera_Forum]

They each serve a purpose. The extern pull-up discussion e.g. has the title max ii device compatibility with 5.0-v cmos devices.

[Altera_Forum]

Dear FvM, 

 Do you mean the example is only more like a voltage shiffter? Can the pull-up resistor not be calculated in the same way as the example? Thank you!   Peter

[Altera_Forum]

The example is in fact for Multi-IO voltage respectively level conversion, it uses the MAX II output in open-drain configuration. In the example, a minimum value based on the available output current is calculated. But in an application, a higher value may be appropriate.