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The receive margin can therefore be expressed as follows.
Receive margin in smart card interface mode:
M = (0.5 –
M: Receive margin (%)
N: Ratio of clock frequency to bit rate (N = 372)
D: Clock duty cycle (L = 0 to 1.0)
L: Frame length (L =10)
F: Absolute deviation of clock frequency
From the above equation, if F = 0 and D = 0.5, the receive margin is as follows.
When D = 0.5 and F = 0:
M = (0.5 – 1/2 × 372) × 100%
= 49.866%
Retransmission: Retransmission is performed by the SCI in receive mode and transmit mode as
described below.
• Retransmission when SCI is in Receive Mode
Figure 13.12 illustrates retransmission when the SCI is in receive mode.
1. If an error is found when the received parity bit is checked, the PER bit is automatically set to
1. If the RIE bit in SCR is set to the enable state, an ERI interrupt is requested. The PER bit
should be cleared to 0 in SSR before the next parity bit sampling timing.
2. The RDRF bit in SSR is not set for the frame in which the error has occurred.
3. If an error is found when the received parity bit is checked, the PER bit is not set to 1 in SSR.
4. If no error is found when the received parity bit is checked, the receive operation is assumed to
have been completed 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.
5. When a normal frame is received, the data pin is held in three-state at the error signal
transmission timing.
444
1
) – (L – 0.5) F –
2N
D – 0.5
(1 + F) × 100%
N
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