topic Re: Port B bit 0 as output on PA4 soic-20 pkg in 8-bit Microcontrollers

Port B bit 0 as output on PA4 soic-20 pkg

CustomSarge — Tue, 04 Aug 2015 12:11:37 GMT

I can't make it drive a ULN2003 (~170uA).

Tried 2 chips, both same syndrome.

Works fine as input, with pull up or not.

Same circuitry using bits 0-5 as outputs, 1-5 behave fine.

With 15+ years using 68xxx08 chips, I think I found my 1st errata.

Am I missing something here? TNX K.Sargent

tonyp — Tue, 04 Aug 2015 16:06:08 GMT

Are you sure this is not of those few pins (usually 2) that are either input-only or output-only? PA4 in some MCUs was that case.

CustomSarge — Wed, 05 Aug 2015 01:44:30 GMT

I scoured the datasheet... no reference.

I'm also 3 for 3... put an soic-20 on a test conversion board.

Put same code (as simple as it gets...) Same Result.

PS Pins typed as input only "shouldn't" reset the cpu on enough pullup to make them behave as outputs...

I had to remap b3 to b0 (a luxury of this design) and it ... works just fine.

Somebody at Freescale needs to step up and tell me I'm wrong or WHAT...

tonyp — Thu, 06 Aug 2015 13:00:07 GMT

I just read the S08PA4 reference which states "PTB0 provide true open drain when operated as output." Hope this helps.

vicentegomez — Thu, 06 Aug 2015 21:01:28 GMT

Hi Tony

yes, this is correct

CustomSarge — Fri, 07 Aug 2015 00:10:41 GMT

Howdy, Yup, I stand corrected. It's logged in:

Pg 139 of RM

Pg 34 of RM (as copied)

Pg 7 of DS note #4

Pg 27 of DS note #2

I was working from the port description section and missed it.

I'd appreciate stuffing a note in the output enable section, at the b0 descriptor.

I'll maintain that when I put enough pullup (1k) to drive the ULN2003,

turning it off (low) reset the processor... odd.

I tried 2.2k, well enough to pull .2mA, but output (as data=1) didn't rise enough.

I saw ~1.5V (Vdd=3.3) when set as output and data=1, not exactly OC behavior,

with nothing connected to pin.

I'm just observing strange stuff, and have no time to do a real proof.

I just remapped b7<->b0 since my b7 was an input, working fine.

Thanks for the guidance (D+ on my incomplete homework...) K.Sargent