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Thus the reception margin in smart card interface mode is given by the following formula.
1
M = (0.5 –
2N
Where M: Reception margin (%)
N: Ratio of bit rate to clock (N = 372)
D: Clock duty (D = 0 to 1.0)
L: Frame length (L = 10)
F: Absolute value of clock frequency deviation
Assuming values of F = 0 and D = 0.5 in the above formula, the reception margin formula is as
follows.
When D = 0.5 and F = 0,
M = (0.5 – 1/2 × 372) × 100%
= 49.866%
Retransfer Operations: Retransfer operations are performed by the SCI in receive mode and
transmit mode as described below.
• Retransfer operation when SCI is in receive mode
Figure 12-8 illustrates the retransfer operation when the SCI is in receive mode.
[1] If an error is found when the received parity bit is checked, the PER bit in SSR is automatically
set to 1. If the RIE bit in SCR is enabled at this time, an ERI interrupt request is generated. The
PER bit in SSR should be kept cleared to 0 until the next parity bit is sampled.
[2] The RDRF bit in SSR is not set for a frame in which an error has occurred.
[3] If no error is found when the received parity bit is checked, the PER bit in SSR is not set to 1.
[4] If no error is found when the received parity bit is checked, the receive operation is judged to
have been completed normally, and the RDRF flag in SSR is automatically set to 1. If the RIE
bit in SCR is enabled at this time, an RXI interrupt request is generated.
[5] When a normal frame is received, the pin retains the high-impedance state at the timing for
error signal transmission.
D – 0.5
) – (L – 0.5) F –
(1 + F) × 100%
N
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