![](http://datasheet.mmic.net.cn/120000/MC68349FT16_datasheet_3559370/MC68349FT16_288.png)
7- 24
MC68349 USER'S MANUAL
MOTOROLA
7.7.1 Byte Transfer Counter Register (BTC)
The BTC is a 32-bit register that contains the number of bytes left to transfer in a given
block. This register is accessible in either supervisor or user space. The BTC can always
be read or written to when the DMA module is enabled (i.e., the STP bit in the MCR is
cleared).
BTC1, BTC2
$794, $7B4
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
A31
A30
A29
A28
A27
A26
A25
A24
A23
A22
A21
A20
A19
A18
A17
A16
RESET:
UUUUUUUUUUUUUUUU
15
14
13
12
11
10
9876543210
A15
A14
A13
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
RESET:
UUUUUUUUUUUUUUUU
U = Unaffected by reset
Supervisor/User
This register is decremented by 1, 2, or 4 for each successful operand transfer from source
to destination locations. When the BTC decrements to zero and no error has occurred, the
CSR DONE bit is set. In the external request mode, the DONE≈ handshake line is also
asserted when the BTC is decremented to zero.
If the operand size is byte, then the register is always decremented by 1. If the operand
size is word and the starting count is even word, the register is decremented by 2. If the
operand size is word and the byte count is not a multiple of 2, the CSR CONF bit is set, and
a transfer does not occur. If the operand size is long word and the count is a multiple of
four, then the register is decremented by 4. If the operand size is long word and the byte
count is not a multiple of 4, the CSR CONF bit is set, and a transfer does not occur. If the
STR bit is set with a zero count in the BTC, the CONF bit is set, and the STR bit is cleared.
When read, this register always contains the count for the next access. If a bus error
terminates the transfer, this register contains the count for the next access that would have
been run had the error not occurred.
7.7.2 Channel Control Register (CCR)
The CCR controls the configuration of the DMA channel. This register is accessible in
either supervisor or user space. The CCR can always be read or written to when the DMA
module is enabled (i.e., the STP bit in the MCR is cleared).
CCR1, CCR2
$788, $7A8
15
14
13
12
11
10
9876543210
INTB
INTN
INTE
ECO
SAPI
DAPI
SSIZE
DSIZE
REQ
BB
S/D
STR
RESET:
UUUUUUUUUUUUUUU0
U = Unaffected by reset
Supervisor/User