Clock - Hitachi H8S/2646 Hardware Manual

14.3.5

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 14-5 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
2n+1
Where: N = Value set in BRR (0 ≤ N ≤ 255)
B = Bit rate (bit/s)
ø = Operating frequency (MHz)
n = See table 14-4
S = Number of internal clocks in 1-bit period, set by BCP1 and BCP0
Table 14-4 Correspondence between n and CKS1, CKS0
n CKS1
0 0
1
2 1
3
Table 14-5 Examples of Bit Rate B (bit/s) for Various BRR Settings
(When n = 0 and S = 372)
N 10.00
0 13441
1 6720
2 4480
Note: Bit rates are rounded to the nearest whole number.
516
× 10
× (N + 1)
CKS0
0
1
0
1
10.714 13.00
14400 17473
7200 8737
4800 5824
6
ø (MHz)
14.285 16.00
19200 21505
9600 10753
6400 7168
18.00 20.00
24194 26882
12097 13441
8065 8961