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
Содержание Am186 CC
Страница 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Страница 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Страница 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Страница 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Страница 39: ...Architectural Overview Am186 CC CH CU Microcontrollers User s Manual 1 15 Figure 1 6 32 Channel Linecard CH CC...
Страница 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Страница 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Страница 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Страница 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Страница 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...