I have the problem that I need to locate the sim-card about 8 meters from the device in which it would normally be installed. As far as I am aware, the devices communicate with the sim card with a serial protocol.

Would it thus be possible to design a extension cable, i.e. with additional line driver on both ends if necessary?

Does anybody have a good (accessible) reference on the signalling and electrical standards of GSM cards?

  • \$\begingroup\$ See addition to answer re Maxim 1840/1841 ICs. \$\endgroup\$ – Russell McMahon Jul 7 '12 at 5:00

(1) below added

(1) MAX1840 / 1841

You can probably find a fairly complete answer to your requirement and a hardware solution for the actual card interface in the MAX1840/1841 and associated data sheet and basic application note . While these ICs are sold principally as level translators and support and protection circuitry to interface with SIM cards, the data sheet contains a wealth of information on timings and levels.

They say

  • The MAX1840/MAX1841 subscriber identity module (SIM)/smart card level translators provide level shifting and electrostatic discharge (ESD) protection for SIM and smart card ports.

    These devices integrate two unidirectional level shifters for the reset and clock signals, a bidirectional level shifter for the serial data stream, and ±10kV ESD protection on all card contacts.

    The MAX1840 includes a SHDN control input to aid insertion and removal of SIM and smart cards, while the MAX1841 includes a system-side data driver to support system controllers without open-drain outputs.

    The logic supply voltage range is +1.4V to +5.5V for the “controller side” and +1.7V to +5.5V for the “card side.” Total supply current is 1.0µA.

    Both devices automatically shut down when either power supply is removed. For a comp l e t e S I M c a r d i n t e r f a c e , c o m b i n e t h e M A X 1 8 4 0 / MA X 1 8 4 1 wi t h t h e MA X 1 6 8 6H 0 V / 3 V / 5 V r e g u l a t e d charge pump. The MAX1840/MAX1841 are available in ultra-small 10-pin µMAX packages that are only 1.09mm high and half the area of an 8-pin SO.

    The MAX1840/MAX1841 are compliant with GSM test specifications 11.11 and 11.12.

Timing information from datasheet:

20 ns/division

enter image description here

1 uS/division.

enter image description here

(2) A SIM card uses a relatively simple hardware interface

The circuit below from "Lady ADA" is from here. I trimmed it only to make it larger when veiwed here. I would expect pin 7 to be speed sensitive as shown here due to RC time constant and pin 2 may be. The rest of the circuit is "somewhat kluged" but shows what is involved. You would want to provide buffering at both ends. but this circuit plus the associated code shows what is required.

enter image description here

The whole SIM reader project can be found here
Eagle schematic and PCB layout provided.
Their product (from the above website):

enter image description here.

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  • \$\begingroup\$ Thanks for this answer. Unfortunately the ressources of the project you reference are extremely thin. There is no rationale for the design choices of the circuit and the software uses a closed source dll. - I am not sure I can learn much that I can translate to another application. Many thanks anyway: maybe further research into sim card readers will produce more info. \$\endgroup\$ – ARF Jul 6 '12 at 14:30
  • \$\begingroup\$ @ArikRaffaelFunke - It looks fairly (or very :-) ) straight forward. Clock on CLK. Data in or out of I/O. RST = direction (I think). \$\endgroup\$ – Russell McMahon Jul 6 '12 at 15:45
  • \$\begingroup\$ Indeed, the physical interface is straight forward. But what about: slew rates, max frequencies, signalling levels, etc... These are crucial for my application. \$\endgroup\$ – ARF Jul 6 '12 at 23:49
  • \$\begingroup\$ @ArikRaffaelFunke - "How hard can it be?" [tm] :-). Max speed will be available somewhere - and it is unlikely to be slower than a Class 4 flash card. Clock slew can be as low as you want with your driver scheme. Data setup and hold when writing are under your control and on reading, anything that the card does would be simple to accommodate. Getting data to and from the far end is a separate problem per se than actually talking to the card and is well covered by any number of standard solutions. \$\endgroup\$ – Russell McMahon Jul 7 '12 at 4:41
  • \$\begingroup\$ @ArikRaffaelFunke ... It would be very easy to set it up at slowish speed and then 'wind it up' while watching signals shapes and timings. If you assume it is a class 4 flash capable card to start and design timings around that I'd guesstimate it would have an excellent chance of working, and may run much faster. There is little reason to think that they'd bother matching Class 10 or better. \$\endgroup\$ – Russell McMahon Jul 7 '12 at 4:43

The specification for GSM SIM cards can be found here in GSM 11-11 although it does state that the electrical interface should conform to ISO/IEC 7861-3 (which you'll have to purchase if you want see the full specification).

There is some good information in this Maxim application note.

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