MCF5249 GPIO Sink Current

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MCF5249 GPIO Sink Current

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tomsaluzzo
Contributor III

How much current can the GPIO pins (pin 23; SDATA3/GPIO56) sink on NXP p/n MCF5249LAG120?

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TomE
Specialist II

Yes, problem that. The Electrical Characteristics are in Chapter 21 of the User Manual. The pin currents are given in Table 21.3. There are three different types of pins, 2mA, 4mA and 8mA. The tables lists SOME of the pins in each category, but doesn't list all of them or the one you're interested in.


The table is broken in other ways. It has Notes 1 through 6, but the "4" reference seems to be missing. There are three current groups (2/4/6 mA) but four capacitance load groups. Normally the high current ones are the high capacitance drivers, but that isn't quite the case here (for instance R/W is 4mA but 20pF). The fact that SDATA3 is in the 20pF group tells you it is probably either 2 or 4mA.

Section 9.8.2 mentions Drive Strength, but then nothing details what they are. "Figure 9-2 General-Purpose Pin Logic for Pin ddata3/gpio34" implies the Drive Strength changes depending on the pin function. That means it might also be different for a pin programmed as GPIO or SDATA.

So the only answer you can get from this manual is "at least 2mA". I would guess that all GPIO pins (or all pins programmed as GPIO) are 2mA. Only the ones that need high drive (like the address bus) have high drive.

The manual was written by Motorola in 2003. A difference version of the manual (maybe even an earlier one) may be more complete. The SCF5249 Rev 3 manual is the same as this one though.

If you look at the previous post to this list, I had similar problems trying to find the Drive Strength for the MCF5235. In that case the IBIS file should have helped, but didn't. For this chip there's no sign of an IBIS file.

Fang Li may be able to answer this one.


Tom

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