Somehow my trusty logic analyzer stopped working this weekend. Running sigrok under WSL is a real pain, so I’m flying blind here.
such as a standard UART), it can be set to 8 bits, 1 even parity bit, 2 stop bits (sometime negotiable to 1, see TC1); during the ATR, the baud rate should be 1/372 of the clock frequency received by the card (corresponding to an ETU of 372 clock cycles)
Wikipedia has as good a description as any.
Setup
- Mode: UART, 9600buad, Even parity, 2 stop bits (I got away with 1)
- PWM connected to clock pin of SIM card. 9600 * 372 = 3.5712MHz
- 1.8volt power supply
- Pull-ups on
- { to open the UART and show data as it arrives
To perform the ATR just pull the SIM RST low (a 1), then release high (@ 1).
3B 9F 95 80 1F C7 80 31 E0 73 FE 21 13 67 22 28 00 40 01 00 01 91
Lycamobile Prepaid SIM-Card (Telecommunication)
http://lycamobile.at
And… it just worked like that! First try. This website has an ATR decoder and database.
It is in fact a LycaMobile SIM that I picked up for free at a grocery store in China Town.
Next steps:
- Some kind of open-drain bidirectional UART setup. Maybe moving the UART TX to the buffer direction pins and inverting the RP2040 pin output.
- See what data we can get out of the card.