DMA Controller
Am186™CC/CH/CU Microcontrollers User’s Manual
8-17
DMA Request from USB
Because USB can use either general-purpose DMA or SmartDMA channels, this is
discussed separately in “DMA and USB” on page 8-43.
8.5.6.6.5
Setting Synchronization
The DSEL bit field in the GDxCON0 register sets the DMA request source for that channel
(see “Selecting DMA Request Sources” on page 8-15). Unlike prior Am186 parts, this bit
also sets the synchronization. General-purpose DMA transfers can be unsynchronized,
source-synchronized, or destination-synchronized.
The source or destination device implies the synchronization type as shown in Table 8-7.
DMA synchronization affects the behavior of the DMA operation and system performance
as a whole. All DMA transfers observe the programmed ready and wait-state conditions for
any chip select active for that cycle.
DRQ must be deasserted before the end of the DMA transfer to prevent another DMA cycle
from occurring. The timing for the required deassertion depends on whether the transfer is
source-synchronized or destination-synchronized.
Unsynchronized Transfers
For unsynchronized DMA transfers, the DRQ signal is internally tied High. When initiated,
an unsynchronized DMA transfer begins immediately and consumes all bus cycles until the
terminal count value in the GDxTC register reaches 0. Unsynchronized DMA is generally
used for copying data between memory locations, between I/O locations, or between
memory and I/O locations. For example, unsynchronized DMA can initialize RAM during
start-up.
Source-Synchronized Transfers
Source-synchronized DMA transfers require either an internally generated DRQ (e.g., from
a UART receiver) or an external device that asserts the associated external DRQ signal for
Table 8-7
General-Purpose DMA Request Source and Synchronization
DMA Request Source
Synchronization Type
Memory or I/O
Unsynchronized
Timer 2
Source
UART Receiver
Source
UART Transmitter
Destination
High-Speed UART Receiver
Source
High-Speed UART Transmitter
Destination
USB Requset Sources
USB Endpoint A Receiver
Source
USB Endpoint A Transmitter
Destination
USB Endpoint B Receiver
Source
USB Endpoint B Transmitter
Destination
USB Endpoint C Receiver
Source
USB Endpoint C Transmitter
Destination
USB Endpoint D Receiver
Source
USB Endpoint D Transmitter
Destination
CU
CC
CC
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...