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6.7.6 Source Address Register (SAR)
The SAR is a 32-bit register that contains the address of the source operand used by the
DMA to access memory or peripheral registers. This register is accessible in either
supervisor or user space. The SAR can always be read or written to when the DMA
module is enabled (i.e., the STP bit in the MCR is cleared).
SAR1, SAR2
$78C, $7AC
26
31
30
29
28
27
25
24
23
22
21
20
19
18
17
16
A31
A30
A29
A28
A27
A25
A24
A23
A22
A21
A20
A19
A18
A17
A16
A26
RESET:
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
A15
A14
A13
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
RESET:
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U = Unaffected by reset
Supervisor/User
During the DMA read cycle, the SAR drives the address on the address bus. This register
can be programmed to increment (CCR SAPI bit set) or remain constant (CCR SAPI bit
cleared) after each operand transfer.
The register is incremented using unsigned arithmetic and will roll over if overflow occurs.
For example, if the register contains $FFFFFFFF and is incremented by 1, it will roll over
to $00000000. This register is incremented by 1, 2, or 4, depending on the size of the
operand and the memory starting address. If the operand size is byte, then the register is
always incremented by 1. If the operand size is word and the starting address is even-
word aligned, then the register is incremented by 2. If the operand size is long word and
the address is even-word aligned, then the register is incremented by 4. The SAR value
must be aligned to an even-word boundary if the transfer size is word or long word;
otherwise, the CSR CONF bit is set, and the transfer does not occur.
When read, this register always contains the next source address. If a bus error
terminates the transfer, this register contains the next source address that would have
been run had the error not occurred.
6.7.7 Destination Address Register (DAR)
The DAR is a 32-bit register that contains the address of the destination operand used by
the DMA to write to memory or peripheral registers. This register is accessible in either
supervisor or user space. The DAR can always be read or written to when the DMA
module is enabled (i.e., the STP bit in the MCR is cleared).
MOTOROLA
MC68340 USER’S MANUAL
6- 33
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