A character that is transmitted over the I/O line is embedded in a character frame.
Before the transmission of a character, the I/O line shall be in state H. Depending upon the convention used, the logical '1' in a character is either represented by state H on the I/O line, direct convention, or state L on the I/O line, inverse convention.
A character consists of 10 consecutive bits (see Figure 7.2
1 start bit in state L;
8 bits, which comprise the data byte;
1 even parity checking bit.
The parity bit is set, in a way, that there is an even number of bits set to '1' including the parity bit in the character frame.
The time origin is fixed as the mean between the last observation of state H and the first observation of state L. The receiver shall confirm the existence of a start bit before 0,7 etu (receiver time). Then the subsequent bits shall be received at intervals of (n + 0,5 ± 0,2) etu (n being the rank of the bit). The start bit is bit 1.
Within a character, the time from the leading edge of the start bit to the trailing edge of the nth bit is (n ± 0,2) etu.
The interval between the leading edges of the start bits of two consecutive characters comprises the character duration (10 ± 0,2) etu, plus a guardtime. Under error free transmission, during the guardtime both the UICC and the terminal shall be in reception mode (I/O line in state H), unless specified otherwise.
The data shall always be passed over the I/O line with the most significant byte first. The order of bits within a byte (that is, whether the least significant or most significant bit is transferred first) is specified in character TS returned in the answer to reset (see ISO/IEC 7816-3 
If the low impedance driver on the I/O line has been selected, as the result of a successful PPS exchange, the following protocol on the I/O line applies.
The transmission state is defined as the period starting from the start bit of the first character to the end of the guardtime of the last character to transmit. During the transmission state the transmitter shall drive the I/O line to the desired level using the low impedance driver, with the exception of the error indication period, e.g. character guardtime of T = 0.
After reception of the last character in a command or response sequence when the communication direction is changed, the entity that is in turn to transmit, terminal or UICC, shall drive the I/O line to the high level using the low impedance driver during the interface inactivity period During clock stop the terminal shall drive the I/O line to high state.
The interface inactivity period ends when the transmission of a new command or its response starts.