Count Register

The Count Register is a critical component of a Direct Memory Access (DMA) engine's control logic. It stores the total number of data units (e.g., bytes, words) to be transferred in a single DMA operation. The register is typically loaded by the CPU or system software to initiate a transfer. During the DMA cycle, the value is decremented as each unit is moved, and the transfer completes when the count reaches zero, often generating an interrupt to signal completion. This register is part of the DMA controller's internal architecture and is not a standalone product; it is integrated into a semiconductor device, typically fabricated on silicon. The register's data width is configurable to match the system bus width, ranging from 8 to 64 bits. The count range for a 32-bit counter is 0 to 4,294,967,295 counts, allowing for large transfers. The count resolution is one count per data unit, meaning the register decrements by one for each unit transferred. The operating frequency is synchronous with the DMA clock, up to 100 MHz. The core logic operates at a supply voltage between 1.8 V and 3.3 V. Dynamic power consumption at maximum frequency ranges from 0.5 mW to 5 mW. The register is designed for industrial-grade operation over a temperature range of -40°C to 85°C, with storage temperature from -55°C to 125°C. It has an ESD tolerance of 2000 V (HBM model) and a latch-up current of 100 mA at 125°C. The package type is QFN-32 with a size of 5×5 mm and a pitch of 0.5 mm, lead-free. These specifications are reference ranges and must be verified with the legal manufacturer for the specific model and application. The Count Register is essential for precise control of data transfers in DMA operations, ensuring efficient data movement without CPU intervention.

The Count Register operates as a down-counter. Upon DMA transfer initiation, it is loaded with the total transfer count. With each successful transfer of a data unit (as dictated by the data width and addressing mode), the register's value is decremented by the appropriate amount (e.g., 1 for byte transfers, 2 for 16-bit word transfers). The DMA controller monitors this value; when it reaches zero, the transfer is considered complete, and the DMA engine typically halts and signals the processor. The register's operation is synchronous with the DMA clock, and its resolution is one count per data unit. The count range supports large transfers, and the data width is configurable to match the system bus. The register's behavior is fundamental to DMA functionality, enabling efficient bulk data movement.