| 摘要 |
<p>PURPOSE:To places devices other than objects of transfer in a stand-by state and reduce the power consumption of a system by comparing the content of a 1st register which specifies a direct memory access channel number to be transferred with the content of a 2nd register stored with a direct memory access channel number current in transfer and sending a stand-by request to the devices which are not in the transfer. CONSTITUTION:When a DMA transfer request from an external peripheral device is detected, a hold request signal is outputted to a CPU. Then when a hold permission signal is inputted from the CPU, an internal control circuit 1 determines a priority level and outputs a DMA permission signal DAK from a bus control circuit 2 to the peripheral device to start DMA transfer. At this time, a DMA transfer cycle is determined by referring to a control register group 8 and an external device is determined by an address register 14. A comparator 11 compares the values of a stand-by channel register 10 and a channel register 9 with each other and sends the stand-by request signal when they match each other.</p> |
