4-58
Registers
Registers: 0x24–0x26
DMA Byte Counter (DBC)
Read/Write
DBC
DMA Byte Counter
[23:0]
This 24-bit register determines the number of bytes
transferred in a Block Move instruction. While sending
data to the SCSI bus, the counter is decremented as data
is moved into the DMA FIFO from memory. While
receiving data from the SCSI bus, the counter is
decremented as data is written to memory from the
LSI53C1000. The DBC counter is decremented each
time data is transferred on the PCI bus. It is decremented
by an amount equal to the number of bytes transferred.
The maximum number of bytes transferred in any one
Block Move command is 16,777,215 bytes. The
maximum value that can be loaded into the
register is 0xFFFFFF. If the instruction is
a Block Move and a value of 0x000000 is loaded into the
DBC register, an illegal instruction interrupt occurs if the
LSI53C1000 is not in the target mode, Command phase.
The
register is also used to
hold the least significant 24 bits of the first Dword of a
SCRIPTS fetch, and to hold the offset value during Table
Indirect I/O SCRIPTS. For a complete description see
Chapter 5, “SCSI SCRIPTS Instruction Set.”
The
power-up value of this register is indeterminate.
23
0
DBC
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Содержание LSI53C1000
Страница 6: ...vi Preface...
Страница 16: ...xvi Contents...
Страница 28: ...1 12 Introduction...
Страница 234: ...4 124 Registers...
Страница 314: ...6 40 Specifications This page intentionally left blank...
Страница 318: ...6 44 Specifications This page intentionally left blank...
Страница 344: ...6 70 Specifications This page intentionally left blank...
Страница 350: ...6 76 Specifications Figure 6 42 LSI53C1000 329 Ball Grid Array Bottom view...
Страница 352: ...6 78 Specifications...
Страница 360: ...A 8 Register Summary...
Страница 376: ...IX 12 Index...