Clock - Renesas H8S/2633 Series Hardware Manual

17.3.5

Clock

Only an internal clock generated by the on-chip 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 17-5 shows some sample bit rates.
If clock output is selected by setting CKE0 to 1, a clock is output from the SCK pin. The clock
frequency is determined by the bit rate and the setting of bits BCP1 and BCP0.
ø
B =
S × 2 × (N + 1)
2n+1
Where: N = Value set in BRR (0 ≤ N ≤ 255)
B = Bit rate (bit/s)
ø = Operating frequency (MHz)
n = See table 17-4
S = Number of internal clocks in 1-bit period, set by BCP1 and BCP0
Table 17-4 Correspondence between n and CKS1, CKS0
n CKS1
0 0
1
2 1
3
Table 17-5 Examples of Bit Rate B (bit/s) for Various BRR Settings
(When n = 0 and S = 372)
N 10.00 10.714
0 13441 14400
1 6720 7200
2 4480 4800
Note: Bit rates are rounded to the nearest whole number.
× 10
6
CKS0
0
1
0
1
13.00 14.285 16.00
17473 19200 21505
8737 9600 10753
5824 6400 7168
ø (MHz)
18.00 20.00
24194 26882
12097 13441
8065 8961
25.00 28.00
33602 37634
16801 18817
11201 12545
785