DMA Controller
8-14
Am186™CC/CH/CU Microcontrollers User’s Manual
cycles. Word transfers to 8-bit address spaces are supported only when the source
decrement or increment is 2 bytes.
The Am186CC/CH/CU microcontrollers have the added feature of being able to transfer by
DMA to and from the UART and High-Speed UART.
The Am186CC and Am186CU microcontrollers can also transfer by DMA to and from USB
peripherals.
Transfering between DMA and peripherals is accomplished by programming the DMA
controller to perform transfers between a data buffer (located either in memory or I/O space)
and the peripheral data register. It is important to note that when a DMA channel is in use
by a peripheral, the corresponding external DMA request signal is deactivated. For a
discussion of using DMA and the on-chip peripherals, see “Selecting DMA Request
Sources” on page 8-15.
8.5.6.5
General-Purpose DMA Terminal Count
Each DMA channel has a 16-bit Transfer Count (GDxTC) register. Software must program
the GDxTC register with the desired number of transfers and set the Terminal Count (TC)
bit in the GDxCON0 register to 1 to enable terminal count. If terminal count is enabled, the
channel performs the requested number of transfers, decrementing the value in the GDxTC
register after each transfer. When the count reaches zero, the DMA transfer terminates.
If the TC bit is 0, the DMA controller decrements the value of GDxTC after each transfer
but does not terminate the transfer when the count reaches zero. The GDxTC register wraps
back to its maximum value and continues decrementing. If the current transfer is an
unsynchronized transfer, DMA terminates when the count reaches zero.
If the Auto Start (AST) bit in the GDxCON0 register is set, DMA resumes transferring every
time the GDxTC register is reloaded with a new value.
When a channel is connected to a USB transmit endpoint, the Am186CC or Am186CU
microcontroller generates a signal internally when the terminal count is reached. The USB
peripheral can use this signal to signal the end-of-packet on a transmit.
8.5.6.6
General-Purpose DMA Channel Operations
The general-purpose DMA control registers (GDxCON0 and GDxCON1) determine the
DMA channel operations. These registers specify the following options:
■
The relative priority of the DMA channel with respect to other DMA channels (see “DMA
Priority” on page 8-9)
■
Whether the DMA resumes a transfer every time the count register is reloaded with a
new value (see “General-Purpose DMA Terminal Count” on page 8-14)
■
Whether the source or destination address is in memory or I/O space (see “General-
Purpose DMA Source and Destination Addresses” on page 8-13)
■
If an interrupt is generated when the transfer count is reached (see “Generating
Interrupts” on page 8-15)
■
Whether bytes or words are transferred (see “Transferring Bytes or Words” on page 8-15)
■
Whether the source or destination address is incremented, decremented, or maintained
constant after each transfer (see “Incrementing or Decrementing Addresses” on
page 8-15)
■
The DMA request source for the channel (see “Selecting DMA Request Sources” on
page 8-15)
CU
CC
CU
CC
Summary of Contents for Am186 CC
Page 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Page 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Page 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Page 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Page 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Page 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Page 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Page 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Page 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...