HD6417660 RENESAS [Renesas Technology Corp], HD6417660 Datasheet - Page 657

• Manufacturer Part Number: HD6417660
• Description: Renesas 32-Bit RISC Microcomputer
• Manufacturer: RENESAS [Renesas Technology Corp]

21.6.2
128 cycles of a 32.768-kHz signal are equal in duration to 125 cycles of a 32-kHz signal. This is
used to convert the 32.768-kHz clock into a 32-kHz clock in the following way. Firstly, the 128
cycles are divided into three states by the counting of cycles, as shown in figure 21.5. State 0 is
made up of the first 43 cycles, state 1 is made up of the next 42 cycles, and state 2 is made up of
the remaining 43 cycles. Then, removing a single falling edge from each of these states leaves 125
cycles. This method realizes 125 cycles from a 32.768-kHz clock within the same period as 125
cycles of the 32-kHz clock. The resulting frequency is 32000 cycles per second. A 32-kHz clock
signal has thus been generated from the converted clock.
The cumulative time differences between each cycle of a 32-kHz signal and the corresponding
cycle of a pseudo-32-kHz signal are shown in figure 21.6. Since the total time for given numbers
of cycles for the 32-kHz clock matches that of the pseudo 32-kHz clock every 125 cycles (see (A)
and (B)), the maximum error is approximately 30 µsec.
(A)
(B)
32.768 kHz
Frequency-Conversion Circuit Operations
Figure 21.5 Function of Frequency-Conversion Circuit
43 cycles
State 0
Stolen
125 cycles
42 cycles
Stolen
State 1
Rev. 1.00, 02/04, page 619 of 804
43 cycles
State 2
Stolen