Honored ContributorI'm using a MAX EPM7128SLC84-15 and need 5V logic outputs. So, the CPLD is wired with all VCC=5V and all the VCCIO = 5V too. Yet the outputs show 3.3V on the 'scope. I believed the Data Sheet pages 2, 6 and 20. What am I doing wrong, please?
Yes, I read a 100+ posts on the Wiki and searched and searched - but no luck ;-) Best wishes - Chosulman.
Honored ContributorAccording to the MAX7000 datasheet (chapter MultiVolt-I/O Interface), external pull-up resistors are required to guarantee 5V CMOS compatible output levels. Without it, a Voh of about 3,8V is achieved with 5V VCCIO.
Honored Contributor@FvM: Thank you! Can you point to the document for this, please; I'm looking at the MAX7000 Programmable Logic Device Family data sheet Sept 2005, ver 6.7 page 20 where there is no mention of external pull-ups ...
Admittedly, I did wonder, and will try it. More later.Honored Contributor@FvM: Later ...
Yes, that did it. Many thanks. The data sheet (pages 20/21) is confusing on this point. My measurements suggest that when in VCCIO = 5V mode, the outputs are actively pulled down to 0V and actively pulled up to 3.3V. Above 3.3V the outputs are open_drain. So your pull up helps you on upwards to 5V, albeit slowly. Curious design ... BTW, the hardware is located in Bochum. Small world! Email me if you're interested in a visit (Sternwarte). [Can't email you - too few posts].Honored ContributorYes, the external pull-up operation is rather slow, unless low, power consuming resistors are used. Are you sure, that you actually need high levels above 3.5V?
Honored ContributorUnfortunately yes. The signals interface with 5V CMOS logic and some signals needed the extra energy to drive it.
Thanks again for your help - and the visit offer's genuine!
