DMA Controller
8-16
Am186™CC/CH/CU Microcontrollers User’s Manual
Figure 8-3
DMA Request Sources
DMA Request from Timer 2
The GDxCON0 register can configure a DMA channel to accept the output of Timer 2 as
a DRQ signal to generate periodic data transfers. Note that this feature generates a DRQ
periodically—even if there is no data. To use this feature, software should program Timer 2
with the T2CON register for “continuous” mode—to reach the maximum count and start
counting again. Each time the timer reaches the maximum count, it generates a single
DRQ. The DMA controller latches the Timer 2 DRQ signal to guarantee that the DMA
channel does not miss the DRQ if the bus is not immediately available (e.g., if a higher
priority DMA has control of the bus). If a second Timer 2 DRQ is generated before the first
request is serviced, the second request is lost.
DMA Request from UARTs
Transfers between the DMA and the UARTs are accomplished by programming the
GDxCON0 register to perform transfers between a data buffer (located either in memory
or I/O space) and a serial port data register (SPTXD, SPRXD, HSPTXD, or HSPRXD).
Note: Using a DMA channel with a UART deactivates the corresponding external DMA
request signal.
For DMA
to the UART or High-Speed UART, specify the following configuration details for
the DMA by writing the address of the register into the GDxDSTL and GDxDSTH registers:
the transmit data register (SPTXD or HSPTXD) address; either I/O-mapped or memory-
mapped; as a byte destination, or word destination if using extended writes. The destination
address (the address of the transmit data register) should remain constant throughout the
DMA operation.
For DMA
from the UART or High-Speed UART, specify the following configuration details
for the DMA by writing the address of the register into the GDxSRCL and GDxSRCH
registers: the receive data register (SPRXD or HSPRXD) address; either I/O-mapped or
memory-mapped; as a byte source, or word source if using extended writes. The source
address (the address of the receive data register) should remain constant throughout the
DMA operation.
UART Receiver
UART Transmitter
High-Speed UART Receiver
High-Speed UART Transmitter
Memory or I/O
USB Endpoint A
USB Endpoint B
USB Endpoint C
USB Endpoint D
DRQ
External DRQ signal
Unsynchronized
Transfer
DMA
DRQ Source Select
Timer 2 (latched)
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...