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
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...