Abstract: A watch dog timer capable of detecting a runaway state of a system including a CPU and DMAC has a watch dog timer and a count clock controller. The watch dog timer counts the number of clock and stores a count result, and transmits a watch dog time out signal to other devices in the system if the number of clocks is over a predetermined value. The count clock controller receives the clock and transmits the clock to the watch dog timer, and halts the transmission of the clock to the watch dog timer when the CPU transmits a bus permission signal to the DMAC.

Abstract: An arithmetic operation processing unit provided with an external program memory storing a high speed instruction group for executing a specific routine of arithmetic operations which require high speed execution is shown. The arithmetic operation processing unit comprises a start address register for holding a starting address of the specific routine of arithmetic operations and an end address register for holding an end address of the specific routine of arithmetic operations, an FIFO type RAM for storing microcodes obtained by decoding the high speed instruction group. The high speed instruction group stored in the program memory is sequentially read out by a first instruction execution control means from the start address to the end address and decoded into corresponding microcodes when a high speed instruction group decoding instruction is executed. The microcodes thus obtained are then stored in the FIFO type RAM.

Abstract: A micro-computer system using a DRAM can refresh the DRAM in a certain interval cycle to maintain the memory contents or refresh the DRAM memory even when the system is set into the standby mode and the clock generator has stopped providing clock timing signals to the memory refreshing circuit. Accordingly, the DRAM memory is refreshed by automatically changing from the interval refresh mode to the self refresh mode when the system operation changes from the normal operation to the standby operation, thus achieving low system power consumption.