Am186™CC/CH/CU Microcontrollers User’s Manual
8-1
CHAPTER
8
DMA CONTROLLER
8.1
OVERVIEW
Direct memory access (DMA) permits the transfer of data between memory and peripherals
without CPU involvement. With DMA transfers, the DMA controller becomes the bus master.
The arbitration for the bus is internal to the processor and is not visible externally. When
the DMA no longer has transfers pending (no internal or external DRQs are asserted) or a
higher priority event occurs, the DMA controller removes its request for the bus thus freeing
the bus for other types of cycles. The type of DMA transfer dictates how long the DMA
controller has control of the bus. However, because a DMA transfer is using the bus, the
processor can be slowed down if it also needs the bus.
Each of the Am186CC/CH/CU microcontrollers contains a DMA controller that provides
both SmartDMA channels and general-purpose DMA channels. The general-purpose DMA
channels can be used for data transfer between memory and I/O spaces (i.e., memory-to-
I/O or I/O-to-memory) or within the same space (i.e., memory-to-memory or I/O-to-I/O). In
addition, the general-purpose DMA controller supports data transfer between some internal
peripherals and memory or I/O.
The SmartDMA channels provide a method for transmission and reception of data across
multiple memory buffers and a sophisticated buffer-chaining mechanism. These channels
are always used in pairs: transmitter and receiver. The transmit channels can only transfer
data from memory to a peripheral; the receive channels can only transfer data from a
peripheral to memory.
The Am186CC microcontroller provides a total of 12 DMA channels: eight SmartDMA
channels and four general-purpose DMA channels. Four of the SmartDMA channels (two
pairs) are dedicated for use with two of the on-board HDLC channels. The remaining four
SmartDMA
channels (two pairs) can support either the third or fourth HDLC channel or
Universal Serial Bus (USB) endpoints A, B, C, or D. On-chip peripherals that support
general-purpose DMA are Timer 2, the two asynchronous serial ports (the UART and the
High-Speed UART), and the USB peripheral controller. External peripherals support DMA
transfers through the external DMA request signals. Each general-purpose channel accepts
a DMA request from one of four sources: the DMA request signals (DRQ1–DRQ0), Timer
2, the UARTs, or the USB peripheral controller. (Note that Timer 2 acts only as a DMA
request source; no data is transferred to or from Timer 2.)
The Am186CH HDLC microcontroller provides a total of eight DMA channels: four
SmartDMA channels (two transmit-receive pairs, 0 and 1) and four general-purpose DMA
channels. The SmartDMA channel pairs are dedicated to the two on-board HDLC channels.
On-chip peripherals that support general-purpose DMA are Timer 2, and the two
asynchronous serial ports (the UART and the High-Speed UART). External peripherals
support DMA transfers through the external DMA request signals. Each general-purpose
channel accepts a DMA request from one of three sources: the DMA request signals
(DRQ1–DRQ0), Timer 2, or the UARTs. (Note that Timer 2 acts only as a DMA request
source; no data is transferred to or from Timer 2.)
The Am186CU USB microcontroller also provides four SmartDMA channels (two transmit-
receive pairs, 2 and 3) and four general-purpose DMA channels. The SmartDMA channel
CC
CH
CU
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...