MC68000 MOTOROLA [Motorola, Inc], MC68000 Datasheet - Page 57

• Manufacturer Part Number: MC68000
• Manufacturer: MOTOROLA [Motorola, Inc]

The DAPR contains 24 (A23–A0) address bits of the destination operand used by the IDMA
to access memory or memory-mapped peripheral controller registers. During the IDMA write
cycle, the address on the master address bus is driven from this register. The DAPR may
be programmed by the DAPI bit to be incremented or remain constant after each operand
transfer.
The register is incremented using unsigned arithmetic and will roll over if overflow occurs.
For example, if a register contains $00FFFFFF and is incremented by one, it will roll over to
$00000000. This register can be incremented by one or two depending on the DSIZE bit and
the starting address.
3.1.2.4 Function Code Register (FCR)
The FCR is an 8-bit register.
The SFC and the DFC bits define the source and destination function code values that are
output by the IDMA and the appropriate address registers during an IDMA bus cycle. The
address space on the function code lines may be used by an external memory management
unit (MMU) or other memory-protection device to translate the IDMA logical addresses to
proper physical addresses. The function code value programmed into the FCR is placed on
pins FC2–FC0 during a bus cycle to further qualify the address bus value.
3.1.2.5 Byte Count Register (BCR)
This 16-bit register specifies the amount of data to be transferred by the IDMA; up to 64K
bytes (BCR = 0) is permitted. This register is decremented once for each byte transferred
successfully. BCR may be even or odd as desired. DMA activity will terminate as soon as
this register reaches zero. Thus, an odd number of bytes may be transferred in a 16-bit op-
erand scenario.
3.1.2.6 Channel Status Register (CSR)
The CSR is an 8-bit register used to report events recognized by the IDMA controller. On
recognition of an event, the IDMA sets its corresponding bit in the CSR (regardless of the
INTE and INTN bits in the CMR). The CSR is a memory-mapped register which may be read
at any time. A bit is cleared by writing a one and is left unchanged by writing a zero. More
than one bit may be cleared at a time, and the register is cleared at reset.
Bits 7–4—These bits are reserved for future use.
MOTOROLA
This register is undefined following power-on reset. The user
should always initialize it and should not use the function code
value “111” in this register.
7
1
7
RESERVED
6
MC68302 USER’S MANUAL
DFC
NOTE
4
4
DNS
1
3
3
BES
2
2
SFC
BED
1
System Integration Block (SIB)
DONE
0
0
3-7