i got a new health-insurance-card last week and i want to read the data of my old card with my arduino.
The card got one of these simcard like chips on it. I figured out it's a SLE4442 Chip. The datasheet says, i have to send data (the read-mode and the memory-adress) first, and then the chip answers.
I also found this tutorial on hackaday.com, but i don't get this part:
The sle4442 has [u]open collector outputs[/u], and depends on pull-up resistors to hold the bus high. Instead of switching the data pin between ground and 5volts, it switches between ground and high-impedance states. High-impedance means that the chip exerts no state on the line, it lets it float, like a microcontroller input pin.
[u]Each of the signal lines need to be pulled-up to 5volts with a 2K-10K resistor[/u], the value isn’t particularly important. Without the pull-up resistor, we’ll never see anything but 0 (ground) on the bus because the sle4442 doesn’t exert a voltage of it’s own. A benefit of this technique is that the Bus Pirate, which only switches at 3.3volts, will talk to the sle4442 at a full 5volts, in compliance with the 3.5volt minimum voltage for a high level (datasheet, page 27, table 3.2.3:Vih).
I thought i know how an open collector output works, but why does the Clock, Reset and Signal-Line use them? Open-collectors are outputs, not inputs? (i thought??)
Anyone a clue on that?