
DMA Controller
9-1
CHAPTER
9
DMA CONTROLLER
9.1
OVERVIEW
Direct memory access (DMA) permits transfer of data between memory and peripherals
without CPU involvement. The DMA unit in the Am186ES and Am188ES microcontrollers
provides two high-speed DMA channels. Data transfers can occur between memory and
I/O spaces (e.g., memory to I/O) or within the same space (e.g., memory-to-memory or I/
O-to-I/O). Either bytes or words can be transferred to or from even or odd addresses on
the Am186ES microcontroller. (The Am188ES microcontroller does not support word
transfers.) Two bus cycles (a minimum of eight clocks) are necessary for each data transfer.
Each channel accepts a DMA request from one of three sources: the channel request pin
(DRQ1–DRQ0), timer 2, or an asynchronous serial port. The two DMA channels can be
programmed with different priorities to resolve simultaneous DMA requests, and transfers
on one channel can interrupt the other channel.
9.2
DMA OPERATION
The format of the DMA control block is shown in Table 9-1. Six registers in the peripheral
control block define the operation of each channel. The DMA registers consist of a 20-bit
source address (2 registers), a 20-bit destination address (2 registers), a 16-bit transfer
count register, and a 16-bit control register.
Table 9-1
DMA Controller Register Summary
The DMA transfer count register (DTC) specifies the number of DMA transfers to be
performed. On the Am186ES, up to 64 Kbytes or 64 Kwords can be transferred with
automatic termination. The Am188ES does not support word transfers.
The DMA control registers define the channel operations (see Figure 9-1). All registers
can be modified or altered during any DMA activity. Any changes made to these registers
are reflected immediately in DMA operation.
Offset from PCB
Register
Mnemonic
Register Name
CAh
D0CON
DMA 0 Control
DAh
D1CON
DMA 1 Control
C8h
D0TC
DMA 0 Transfer Count
D8h
D1TC
DMA 1 Transfer Count
C6h
D0DSTH
DMA 0 Destination Address High
D6h
D1DSTH
DMA 1 Destination Address High
C4h
D0DSTL
DMA 0 Destination Address Low
D4h
D1DSTL
DMA 1 Destination Address Low
C2h
D0SRCH
DMA 0 Source Address High
D2h
D1SRCH
DMA 1 Source Address High
C0h
D0SRCL
DMA 0 Source Address Low
D0h
D1SRCL
DMA 1 Source Address Low
Содержание Am186 ES
Страница 1: ...Am186 ES and Am188 ES User s Manual...
Страница 4: ...iv...
Страница 12: ...Table of Contents xii...
Страница 22: ...Features and Performance 1 8...
Страница 60: ...System Overview 3 28...
Страница 84: ...Chip Select Unit 5 14...
Страница 132: ...Timer Control Unit 8 8...
Страница 166: ...Programmable I O Pins 11 6...
Страница 184: ...Register Summary A 18...