Datasheet

Section 15 Smart Card Interface
Rev.6.00 Sep. 27, 2007 Page 684 of 1268
REJ09B0220-0600
15.3.5 Clock
Only an internal clock generated by the built-in baud rate generator can be used as the
transmit/receive clock for the smart card interface. The bit rate is set with BRR and the CKS1,
CKS0, BCP1, and BCP0 bits in SMR. The formula for calculating the bit rate is as shown below.
Table 15.5 shows some sample bit rates.
If clock output is selected by setting CKE0 to 1, the clock is output from the SCK pin. The clock
frequency is determined by the bit rate and the setting of bits BCP1 and BCP0.
B =
φ
S × 2
2n+1
× (N + 1)
× 10
6
Where: N = Value set in BRR (0 ≤ N ≤ 255)
B = Bit rate (bits/s)
φ = Operating frequency (MHz)
n = See table 15.4
S = Number of internal clock cycles in 1-bit period set by bits BCP1 and BCP0
Table 15.4 Correspondence between n and CKS1, CKS0
n CKS1 CKS0
0 0 0
1 1
2 1 0
3 1
Table 15.5 Examples of Bit Rate B (bits/s) for Various BRR Settings
(When n = 0 and S = 372)
φ (MHz)
N 10.00 10.714 13.00 14.285 16.00 18.00 20.00 25.00
0 13441 14400 17473 19200 21505 24194 26882 33602
1 6720 7200 8737 9600 10753 12097 13441 16801
2 4480 4800 5824 6400 7168 8065 8961 11201
Note: Bit rates are rounded to the nearest whole number.