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2014-01-23 - an0820_Rev1.00
5
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The pull resistor used in the EFM32-implementation is the internal pull-up in the EFM32's GPIO pin.
2.2.2 Power Up, Clock and Reset
When a card is inserted into the reader, all the contacts are disconnected from the terminal/reader,
including ground. The reason for this is that the contacts in the terminal slide over the smart card contacts
while the card is inserted. Applying power to the wrong pins could in theory damage the card or the
reader. When the card is properly inserted, there is usually an electrical contact that breaks connection,
indicating to the reader that the card is fully inserted. Now the reader initiates a power on and reset
sequence.
The interface is responsible for the timing of the sequence. The most important parameters are the clock-
cycle count before and after reset is released. The interface should enable the clock and keep it running
for 40k cycles before reset is released. After reset, the card must respond with its ATR within a window
of 400-40000 clock cycles. The timing is illustrated in Figure 2.3 (p. 5)
Figure 2.3. Answer to Reset Sequence
Card
Insert ed
Power
enabled, IO-
pin pulled high
Clock
St art ed
Reset
Released
ATR
Received
Vcc
Clk
Reset
IO
ATR- Dat a
Clock Running
Wait 40 000
clock cycles
< 40 000
clock cycles
2.2.3 Byte Transfers
During the power on and reset sequence, the smart card answers with its "Answer to Reset". The
transmission of this first data-packet is carried out with default communication parameters listed below:
• Baud rate = F
clock
/372. Clock should be approximately 3.57 MHz, resulting in 9.6 kBaud/s.
• 8 data bits.
• 1 start bit.
• 1 parity bit, even.
• 1.5 stop bits (guard period for Ack/Nack).
• Coding of 0's and 1's: This can vary, the correct naming of this is: "Direct" or "Inverse" convention. It
is based on the very first character transmitted, called TS. "Direct" indicated by TS=HLHHLHHHLLH
(H = Vdd, L = GND) means that the following data is transferred as 0=GND, 1=Vdd and with the least
significant bit first. For the Inverse convention, indicated by TS=HLHHLLLLLLH, data is transmitted
with most significant bit first and 0=Vdd, 1=GND.
Using the above parameters, the interface must also adhere to the Ack/Nack of bytes, based on the
parity bit. A Nack is indicated when the receiver pulls the data line low in the guard period after the parity
bit is transmitted. If this happens, the transmitter should immediately retransmit the last byte.
One bit-period is called an "Elementary Time Unit" or ETU, this is used throughout the 7816 standard as a
basis for defining the timing of the protocol. An illustration of one transmitted byte is given in Figure 2.4 (p.
6) .
Summary of Contents for EFM32
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