Honored Contributor
Honored ContributorI apologize for confusing the discussion with telling about pull-up resistors. They are of-course pull-down resistors.
The configuration operation for packages without MSEL[3] can't be explained by pull-up or pull-down resistors. I had to read the Cyclone III handbook thorougly to figure out what they are doing here. After reviewing the topic, I completely agree with baldur, that Altera doesn't manage to give an understandable explanation. I found a simple explanation, however. Just read the device handbook literally: --- Quote Start --- The AS Fast POR configuration scheme at 3.0- or 2.5-V configuration voltage standard and the AP configuration scheme are not supported in Cyclone III devices without the MSEL[3] pin. To configure these devices with other supported configuration schemes, select the MSEL[2..0] pins according to the MSEL settings in Table 9–7. --- Quote End --- Table 9.7 is refering to the Rev. 3 Handbook. If you wipe-out the unsupported AP and "Fast" AS 2.5/3.0V from the table and ignore the Cyclone III LS related entries, 7 unique codings of MSEL[2..0] are left over. All have MSEL[3] = MSEL[2]. So obviously MSEL[3] is bonded to the MSEL[2] pin. If this explanation is right (I'm rather sure about), why it's not simply written in the device handbook?
