TMS320F28335: Why is the GPIO port showing "HIGH" even the code was erased from the TMS320F28335

Yue Li2

Part Number: TMS320F28335
Other Parts Discussed in Thread: UNIFLASH, , TMS320F2811

Hello,

I am using TMS320F28335ZJZQ in my board. It is a new board, so after testing some code, I erased the code in the DSP with the software "UniFlash". However, I found the pin C6 (GPIO46/XA6), the GPIO port, still output 3.3V after the erasing.

Could that be "not-erasing the code completely" or some other issues?

(BTW, I have another board using LF2811 DSP. I used UniFlash to erase it . The code is clean or at least the related GPIO does not output 3.3V at all)

Thanks for your advice in advance!!

over 8 years ago

0 Adam Haun over 8 years ago

TI__Expert 8950 points

On reset, the pins are inputs with pull-ups enabled (except on the PWM GPIOs). If GPIO46 is undriven, the pull-ups will bring it to 3.3V.

0 Yue Li2 over 8 years ago in reply to Adam Haun

Intellectual 640 points

HI Adam

Thank you for your response!

Do you mean that,even for a totally new TMS320F28335, when I apply the working voltages for the chip, say 3.3V and 1.9V, for "non-PWM GPIOs", will have 3.3V? Can you please point out which part in the datasheet or tech manual describes that?

Is that the feature of TMS320F28335 only? Because I didn't see it at TMS320F2811 whose GPIOs are 0V if I have no code in it.

Thanks, again!

0 Adam Haun over 8 years ago in reply to Yue Li2

TI__Expert 8950 points

You can see it in the reset values of the registers. If you look in the system control guide (literature number SPRUFB0), you can see that GPADIR, GPBDIR, and GPCDIR start out at all zeros -- inputs. GPAPUD, GPBPUD, and GPCPUD are all zeros (pull-ups enabled) except for GPIO0-11.

0 Yue Li2 over 8 years ago in reply to Adam Haun

Intellectual 640 points

Adam-

I missed the part in SPRUFB0. Thank you for pointing out for me.

I noticed that for GPAPUD, GPBPUD indicated that the "Enable the internal pullup on the specified pin (default)", however, there is no "default" mentioned in GPCPUD. So, for GPCPUD,by default, is the internal pullup enabled for GPIO64 - 87?

Thanks, again!

0 Adam Haun over 8 years ago in reply to Yue Li2

TI__Expert 8950 points

You can always tell the default value of a bit or field by looking at the figure for the register. Below the field, it will say something like "R/W-0" or "R/W-1". The number indicates the reset state.

0 Yue Li2 over 8 years ago in reply to Adam Haun

Intellectual 640 points

Adam,

Thank you so much for your help!

I am doing the similar research for TMS320x281x DSP system control and interrupts reference guide (SPRU078G). However, there is no clear indication of the GPIOs who have internal pullup and who haven't.

Could you please tell me where I can find such info for TMS320x281x DSP?

Thanks!

0 Adam Haun over 8 years ago in reply to Yue Li2

TI__Expert 8950 points

The pull-ups and pull-downs on the 281x devices are not configurable. You can see which pins have pull-ups, which have pull-downs, and which have no pull in the datasheet (SPRS174). Look in section 2.4 (Introduction -> Signal Descriptions).

0 Yue Li2 over 8 years ago in reply to Adam Haun

Intellectual 640 points

Adam,

That confuses me. what do you mean "not configurable". Is there any chip such as F28335's pin's pulllup or pulldown configurable?

Also, I test one of our boards with F2811. I can see clearly for GPIOB0, when there is no code in the chip, the pin's voltage level is 0 (this pin has internal pullup -- PU). But for similar GPIO pin in F28335, even there is no code in the chip, if such GPIO has internal pullup, the voltage level is HIGH.

Is there any parts I missed?

Thanks!!

0 Adam Haun over 8 years ago in reply to Yue Li2

TI__Expert 8950 points

No C2000 device lets you choose between pull-up and pull-down. But on the 281x devices, I don't think you can turn the pull-ups and pull-downs off. I'm not sure why GPIOB0 would be low. I haven't worked on the older devices much, so I've asked a couple of my coworkers to answer this question.

0 Manoj Santha Mohan over 8 years ago in reply to Adam Haun

TI__Guru 55700 points

In F281x devices, GPIOB0 has an internal pull up. On reset and with erase flash, you should see this pin pulled up.

Is this pin felt floating (or) connected to external circuitry?

Is your observation an isolated one (or) you see on every F281x boards?