MOTOROLA
MC68341 USER'S MANUAL
6- 7
6.4 DATA TRANSFER MODES
The DMA channel supports single- and dual-address transfers. The single-address transfer
mode consists of one DMA bus cycle, which allows either a read or a write cycle to occur.
The dual-address transfer mode consists of a source operand read and a destination
operand write. Two DMA bus cycles are executed for the dual-address mode: a DMA read
cycle and a DMA write cycle.
6.4.1 Single-Address Mode
The single-address DMA bus cycle allows data to be transferred directly between a device
and memory without going through the DMA. In this mode, the operand transfer takes place
in one bus cycle, where only the memory is explicitly addressed. The DMA bus cycle may
be either a read or a write cycle. The DMA provides the address and control signals
required for the operation. The requesting device either sends or receives data to or from
the specified address. Only external requests can be used to start a transfer when the
single-address mode is selected. An external device uses DREQ≈ to request a transfer.
Each DMA channel can be independently programmed to provide single-address transfers.
The CCR ECO bit controls whether a source read or a destination write cycle occurs on the
data bus. If the ECO bit is set, the external handshake signals are used with the source
operand and a single-address source read occurs. If the ECO bit is cleared, the external
handshake signals are used with the destination operand, and a single-address destination
write occurs. The channel can be programmed to operate in either burst transfer mode or
cycle steal mode. See 6.7 Register Description for more information.
6.4.1.1 SINGLE-ADDRESS READ. During the single-address source (read) cycle, the
DMA controls the transfer of data from memory to a device. The memory selected by the
address specified in the source address register (SAR), the source function codes in the
function code register (FCR), and the source size in the CCR provides the data and control
signals on the data bus. This bus cycle operates like a normal read bus cycle. The DMA
control signals (DACK≈ and DONE≈) are asserted in the source (read) cycle. See Figures
6-5 and 6-6 for timing diagrams single-address read for external burst and cycle steal
modes.
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Freescale Semiconductor, Inc.
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