12 Replies Latest reply on Apr 20, 2018 7:20 AM by e.pratt_1639216

Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

user_483038750 Apr 17, 2018 12:59 AM

Hello,

Do SWDIO and SWDCLK for PSoC4/4S/4A need external pull-up resistors in case of the mass production?

And What ohms do you recommend?

Best regards,

Yocchi

1. Re: Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

BrandonP_16 Apr 17, 2018 1:56 AM (in response to user_483038750)

Hi Yocchi,

SWD lines (SWDIO and SWDCLK) are usually using for FW programming and debugging with PC.
In addition, when you program or debug with PC, MiniProg3 or TT-Bridge is necessary for its connection that external pull-up registers are mounted on this kit already.

So, in mass production (or FW development), SWD lines do not need to mount external pull-up resistors.

Thanks,
Brandon
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2. Re: Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

user_483038750 Apr 17, 2018 2:02 AM (in response to BrandonP_16)

Hello Brandon-san,

Thank you for your reply.
What is this kit?
I am thinking that the circuit is own.

Best regards,
Yocchi
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3. Re: Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

BrandonP_16 Apr 17, 2018 2:37 AM (in response to user_483038750)

Yocchi-san,

For programming, PSoC needs MiniProg3 kit to connect between PSoC and PC.
Please refer below link for MiniProg3.
CY8CKIT-002 PSoC® MiniProg3 Program and Debug Kit

Thanks,
Brandon
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4. Re: Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

user_483038750 Apr 17, 2018 2:50 AM (in response to BrandonP_16)

Hello Brandon-san,

I know what you mean.
But, I tell you because it runs without the debugger(miniprog3) as a product.
Do you know what I mean?

Best regards,
Yocchi
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5. Re: Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

BrandonP_16 Apr 17, 2018 2:58 AM (in response to user_483038750)

Hi Yocchi-san,

You mean the host processor(or external processor) will program the PSoC4 without MiniProg3?

Thanks,
Brandon
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6. Re: Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

user_483038750 Apr 17, 2018 3:02 AM (in response to BrandonP_16)

Hello Brandon-san,

No, the application software of PSoC4/4S/4A is running with no connection to SWD.

Best regards,
Yocchi
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7. Re: Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

BrandonP_16 Apr 17, 2018 4:13 AM (in response to user_483038750)

Hi Yocchi-san,

Yes, application software (I said FW) is running with no connection to SWD. SWD lines are used only for programming and debugging.
Then, why do you consider the external pull-up resistors in mass production? I'm really eager to know what is your problem.

Thanks,
Brandon
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8. Re: Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

e.pratt_1639216 Apr 17, 2018 7:41 AM (in response to user_483038750)

There are 3rd party companies that build devices for mass-production of boards with the PSoC programmed on all of the boards simultaneously to speed up production times. See here: Device Programmer System Partners
Otherwise, all you need for programming the device is to have the SWD pins connected to a programmer (like the Miniprog3), power the board (Miniprog3 has the option to power the board through the SWD pins), and then program the FW image you want on the board.
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9. Re: Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

user_483038750 Apr 17, 2018 4:20 PM (in response to e.pratt_1639216)

Hello Brandon-san,

SWDCLK is input and SWDIO is input/output.
If the application of PSoC4/4S/4A is running, may we leave input and input/output pin without pull-up or pull-down?

Best regards,
Yocchi
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10. Re: Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

e.pratt_1639216 Apr 18, 2018 8:58 AM (in response to user_483038750)

Yes, you may the pins without the pull-up or pull-down.
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11. Re: Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

user_483038750 Apr 18, 2018 4:39 PM (in response to e.pratt_1639216)

Hi,

Thank you for your reply.
Why do not we need to input pull-up or pull-down resistor?
Are there pull-up or pull-down internally?

Best regards,
Yocchi
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12. Re: Do SWDIO and SWDCLK need external pull-up resistors in case of mass production?

e.pratt_1639216 Apr 20, 2018 7:20 AM (in response to user_483038750)

I believe the SWD are unconfigured during reset, and the SWD protocol resets the chip to achieve the changed pin state for communication to work. This would be an internal pullup (or no pullups) when the SWD acquires the device. It is all listed in the technical reference manual: http://www.cypress.com/file/126171/download
The pins are set to the pullup/Hi-z/strong drive internally by the chip during the SWD acquire procedure, which is why the pins can be reused for GPIO when not programming. The pin uses a 100k ohm pullup on the data line (not sure if the other pins use any pullups).
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