uPD789074 Subseries 8-Bit Single-Chip Microcontrollers UD - Home

CHAPTER 5 CLOCK GENERATOR5.5 Clock Generator OperationThe clock generator generates the following clocks and controls the operation modes of the CPU, such asstandby mode.• System clock• CPU clockfXfCPU• Clock to peripheral hardwareThe operation of the clock generator is determined by the processor clock control register (PCC) as follows.(a)The slow mode (0.8 µs: at 10.0 MHz operation/1.6 µs: at 5.0 MHz operation) of the system clock is selectedwhen the RESET signal is generated (PCC = 02H). While a low level is input to the RESET pin, oscillationof the system clock is stopped.(b)Two types of minimum instruction execution time (0.2 µs, 0.8 µs: at 10.0 MHz operation/0.4 µs, 1.6 µs: at5.0 MHz operation) can be selected by the PCC setting.(c)Two standby modes, STOP and HALT, can be used.(d)The clock for the peripheral hardware is generated by dividing the frequency of the system clock. Therefore,the peripheral hardware stops when the system clock stops (except for an external input clock).80User’s Manual U14801EJ3V1UD