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Section 14 Smart Card Interface
From this equation, if F = 0 and D = 0.5 the receive margin is as follows.
D = 0.5, F = 0
M = {0.5 – 1/(2 × 372)} × 100%
= 49.866%
Retransmission: Retransmission is described below for the separate cases of transmit mode and
receive mode.
• Retransmission when SCI is in Receive Mode (See Figure 14.11)
1. The SCI checks the received parity bit. If it detects an error, it automatically sets the PER
flag to 1. If the RIE bit in SCR is set to the enable state, an ERI interrupt is requested. The
PER flag should be cleared to 0 in SSR before the next parity bit sampling timing.
2. The RDRF bit in SSR is not set to 1 for the error frame.
3. If an error is not detected when the parity bit is checked, the PER flag is not set in SSR.
4. If an error is not detected when the parity bit is checked, receiving operations are assumed
to have ended normally, and the RDRF bit is automatically set to 1 in SSR. If the RIE bit in
SCR is set to the enable state, an RXI interrupt is requested. If RXI is enabled as a DMA
transfer activation source, the RDR contents can be read automatically. When the DMAC
reads the RDR data, it automatically clears RDRF to 0.
5. When a normal frame is received, at the error signal transmit timing, the data pin is held in
the high-impedance state.
Ds D0 D1 D2 D3 D4 D5 D6 D7 Dp
RDRF
PER
Rev. 3.00 Mar 21, 2006 page 518 of 814
REJ09B0302-0300
Frame n
DE
(2)
(1)
Figure 14.11 Retransmission in SCI Receive Mode
Retransmitted frame
Ds D0 D1 D2 D3 D4 D5 D6 D7 Dp
Frame n + 1
(DE)
Ds
D0 D1 D2 D3 D4
(4)
(3)
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