topic Re: Transmit data from SMARTCARD0 interface, I/O in open-drain? in LPC Microcontrollers

Transmit data from SMARTCARD0 interface, I/O in open-drain?

kovalenkoi — Fri, 17 Jan 2020 15:09:42 GMT

I am realising ISO7816-3 SmartCard interface with level translator. I am using MCU LPC54608 and TXB0104 as level translator. Power level on smart card - 3.0V (Class B), voltage level on MCU - 3.3V. In future also need support Class A (5.0V) and Class C (1.8V). In MCU side I/O pin have pull-up resistor 100k, in SmartCard side pull-up 100k too.

I correct receive ATR, oscillograme of it (clock frequency 2MHz):

But, if I try to send data to interface, I see this (data byte 0xAA):

I see, that data transmited, but translator switch from 1 to 0 and locked in this state.

If I didn't setup "Smart Card Interface Enable" bit in SCICTRL register, I have this oscillograme:

Thus levels sets ok.

Also, in experiments with SC0IO pin (P0.20) in GPIO-mode, I made a state transition table:

Switch Pin State L to Pin State H, then real bus level H.
Switch Pin State H to Pin State L, then real bus level L.
Switch Pin State Z to Pin State L, then real bus level L.
Switch Pin State Z to Pin State H, then real bus level H.
Switch Pin State L to Pin State Z, then real bus level L. No switching! Because translator so work.
Switch Pin State H to Pin State Z, then real bus level H.

So I conclude, that SC0IO in SmartCard mode work as Open-Drain. But open-drain pins (and L-Z pin-switching) - features of I2C or iButton interfaces, in ISO7816-3 this did not use!

Without TXB0104 and speed setup TA=0x96 (clock frequency 5MHz, etu value is 16) and pull up 100k, I have this oscillograme on transmit:

This confirms, that IO pin work in Open-Drain mode.

Questions:

How I can use SMARTCARD interface in push-pull mode?
Chapter 31.5.11 of UM10912 recommended push-up resistor on I/O pin. What value should be this resistor for big baudrates (TA=0x96 or TA=0x97, i.e. ~300bps and 600bsp) on smartcard bus?
What the level translator recommended by NXP?

SmartCard interface initialization example in attach.

Re: Transmit data from SMARTCARD0 interface, I/O in open-drain?

FelipeGarcia — Tue, 21 Jan 2020 17:09:27 GMT

Hello,

Please check below image, 20 Kohm resistors are recommended. For push-pull output you can change OD bit in IOCON registers. Here you will change pen-drain output or push-pull output.

Regarding the level translator, I am not expert in this matter so I recommend you to create a different question with a detail description in the community space below.

Other NXP Products

Best regards,

Felipe

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Re: Transmit data from SMARTCARD0 interface, I/O in open-drain?

kovalenkoi — Wed, 22 Jan 2020 10:11:17 GMT

This code:
// Program IOCON register to select the SCIn_IO function.
IOCON_PinMuxSet(IOCON, PORT_NUM__SMART_CARD_IO, PIN_NUM__SMART_CARD_IO,
IOCON_FUNC5 | /* Pin is configured as SCI0_IO */
  IOCON_MODE_INACT | /* No addition pin function */
  IOCON_DIGITAL_EN | /* Enables digital function */
  IOCON_INPFILT_OFF | /* Input filter disabled */
  IOCON_OPENDRAIN_EN /* TEST TEST TEST */
  ); /* I/O as SCIO */

and this:
// Program IOCON register to select the SCIn_IO function.
IOCON_PinMuxSet(IOCON, PORT_NUM__SMART_CARD_IO, PIN_NUM__SMART_CARD_IO,
  IOCON_FUNC5 | /* Pin is configured as SCI0_IO */
  IOCON_MODE_INACT | /* No addition pin function */
  IOCON_DIGITAL_EN | /* Enables digital function */
  IOCON_INPFILT_OFF | /* Input filter disabled */
  ); /* I/O as SCIO */
no effect, in SC-interface mode always Open-Drain mode! As I understand, in IOCON-mode FUNC5, OD-bit didn't actual .

In You picture 20k pull-up sets on SCLK. My question about SCIO-line.

Re: Transmit data from SMARTCARD0 interface, I/O in open-drain?

kovalenkoi — Fri, 24 Jan 2020 09:36:40 GMT

If compare documentation on LPC11U and LPC54xxx familys, then we can see:

We see, that in LPC11Uxx SCIO pin (USART TXD) work as open-drain. In LPC54xxx this information didn't present. But my issue show that in LPC54xxx SCIO work as open-drain too.

It fact very important for choosing level translator.