Specifications

DMA Controller (V40)
DMA Base Count/Current Count (DBC/DCC)
Two DBC/DCC registers make up the 16-bit DMA count, as shown in
Figure 9-4. The two DBC/DCC registers can be accessed with byte or
word instructions. The function of these registers depends on the
BASE bit of the DCH register. If the BASE bit is set to a logical 0,
the values written to the Count registers are programmed into both
base and current count values. The current count is read from the
Count registers if the BASE bit is set to a logical 0. If the BASE bit is
set to a logical 1, the values written to the Count registers are
programmed into the base value only. The base value is read from the
Count registers if the BASE bit is set to a logical 1.
Register:DBC/DCC - Low
Address:Base + 2
Access:Read or Write
76543210
C0C1C2C3C4C5C6C7
Register:DBC/DCC - High
Address:Base + 3
Access:Read or Write
76543210
C8C9C10C11C12C13C14C15
Figure 9–4. DMA Base and Current Count Registers.
9-10