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Thus the receive margin in asynchronous mode is given by the following formula.
1
M = (0.5 –
) – (L – 0.5) F –
2N
Where M: Receive margin (%)
N: Ratio of bit rate to clock (N = 32, 64, 372, 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 receive 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 13-11 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.
[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 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 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.
Rev. 5.00, 12/03, page 514 of 1088
D – 0.5
(1 + F) × 100%
N
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