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Thus the reception margin in asynchronous mode is given by the following formula.
Formula for reception margin in smart card interface mode
1
M = (0.5 –
2N
Where M: Reception margin (%)
N: Ratio of bit rate to clock (N = 32, 64, 372, and 256)
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, D = 0.5 and N = 372 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 (Except Block Transfer Mode): 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 17-11 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.
If DMAC or DTC data transfer by an RXI source is enabled, the contents of RDR can be read
automatically. When the RDR data is read by the DMAC or DTC, the RDRF flag is
automatically cleared to 0.
[5] When a normal frame is received, the pin retains the high-impedance state at the timing for
error signal transmission.
) – (L – 0.5) F –
D – 0.5
(1 + F) × 100%
N
689
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