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SYM53C876/876E Data Manual
SCSI SCRIPTS Instruction Set
Memory Move Instructions
These bits are reserved and must be zero. If
any of these bits is set, an illegal instruction
interrupt occurs.
Bit 24
No Flush
Note: This bit has no effect unless the Pre-fetch
Enable bit in the DCNTL register is set.
For information on SCRIPTS instruction
prefetching, see Chapter 2.
When this bit is set, the SYM53C876 performs a
Memory Move without flushing the prefetch unit.
When this bit is clear, the Memory Move instruc-
tion automatically flushes the prefetch unit. Use
the No Flush option if the source and destination
are not within four instructions of the current
Memory Move instruction.
Bits 23-0
Transfer Count
The number of bytes to transfer is stored in
the lower 24 bits of the first instruction word.
Read/Write System Memory from a Script
By using the Memory Move instruction, single or
multiple register values are transferred to or from
system memory.
Because the SYM53C876 responds to addresses
as defined in the Base I/O or Base Memory regis-
ters, it can be accessed during a Memory Move
operation if the source or destination address
decodes to within the chip’s register space. If this
occurs, the register indicated by the lower seven
bits of the address is taken as the data source or
destination. In this way, register values are saved
to system memory and later restored, and
SCRIPTS can make decisions based on data val-
ues in system memory.
The SFBR is not writable via the CPU, and there-
fore not by a Memory Move. However, it can be
loaded via SCRIPTS Read/Write operations. To
load the SFBR with a byte stored in system mem-
ory, first move the byte to an intermediate
SYM53C876 register (for example, a SCRATCH
register), and then to the SFBR.
The same address alignment restrictions apply to
register access operations as to normal memory-
to-memory transfers.
Second Dword
Bits 31-0
DSPS Register
These bits contain the source address of the
Memory Move.
Third Dword
Bits 31-0
TEMP Register
These bits contain the destination address for
the Memory Move.