Attaching a Direct Memory Device to a Single Chip Microprocessor Using an Internal or an External Random-Access Memory
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
A technique is described whereby a peripheral device requiring Direct Memory Access (DMA) activity, with either internal or external Random-Access Memory (RAM), may be attached to a single-chip microprocessor having a no hold request input, such as an Intel 8051. Fig. 1 shows the attachment of the peripheral device requiring DMA activity with the internal RAM interconnected to the microprocessor. The two-channel DMA device requests an interrupt input 1 to the microprocessor. This signal is also attached to an on-chip counter input 2. The counters serve as terminal count registers for the respective channels. They are software preloaded with a value corresponding to the maximum number of DMA cycles required for the respective channels. Each successive DMA cycle increments the counter until an overflow occurs.