Block Transfer Mode; Receive Data Sampling Timing And Reception Margin - Renesas H8S Series Hardware Manual

For the inverse convention type, logic levels 1 and 0 correspond to states A and Z, respectively
and data is transferred with MSB-first as the start character, as shown in figure 15.24. Therefore,
data in the start character in the figure is H'3F. When using the inverse convention type, write 1 to
both the SDIR and SINV bits in SCMR. The parity bit is logic level 0 to produce even parity,
which is prescribed by the smart card standard, and corresponds to state Z. Since the SINV bit of
this LSI only inverts data bits D7 to D0, write 1 to the O/E bit in SMR to invert the parity bit in
both transmission and reception.
15.7.3

Block Transfer Mode

Block transfer mode is different from normal smart card interface mode in the following respects.
• If a parity error is detected during reception, no error signal is output. Since the PER bit in
SSR is set by error detection, clear the bit before receiving the parity bit of the next frame.
• During transmission, at least 1 etu is secured as a guard time after the end of the parity bit
before the start of the next frame.
• Since the same data is not re-transmitted during transmission, the TEND flag in SSR is set
11.5 etu after transmission start.
• Although the ERS flag in block transfer mode displays the error signal status as in normal
smart card interface mode, the flag is always read as 0 because no error signal is transferred.
15.7.4

Receive Data Sampling Timing and Reception Margin

Only the internal clock generated by the internal baud rate generator can be used as a
communication clock in smart card interface mode. In this mode, the SCI can operate using a
basic clock with a frequency of 32, 64, 372, or 256 times the bit rate according to the BCP1 and
BCP0 settings (the frequency is always 16 times the bit rate in normal asynchronous mode). At
reception, the falling edge of the start bit is sampled using the internal basic clock in order to
perform internal synchronization. Receive data is sampled at the 16th, 32nd, 186th and 128th
rising edges of the basic clock pulses so that it can be latched at the center of each bit as shown in
figure 15.25. The reception margin here is determined by the following formula.
M =  (0.5 –
M: Reception 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 rate deviation
1
) – (L – 0.5) F –
2N
Section 15 Serial Communication Interface (SCI, IrDA)
 D – 0.5 
(1 + F)  × 100 [%]
N
Rev. 3.00 Jul. 14, 2005 Page 483 of 986
... Formula (1)
REJ09B0098-0300