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Instruction Set of the I/O Processor
I/O Instructions
6-8
SYM53C810A Data Manual
Second Dword
Bits 31-0 Start Address
T his 32-bit field specifies the starting address
of the data to be moved to/from memory. T his
field is copied to the DNAD register. When the
SYM53C810A transfers data to or from mem-
ory, the DNAD register is incremented by the
number of bytes transferred.
When bit 29 is set, indicating indirect address-
ing, this address is a pointer to an address in
memory that points to the data location. When
bit 28 is set, indicating table indirect address-
ing, the value in this field is an offset into a
table pointed to by the DSA. T he table entry
contains byte count and address information.
I/O Instructions
T he I/O SCRIPT S instruction causes the
SYM53C810A to trigger common SCSI hardware
sequences such as Set/Clear ACK , Set/Clear AT N,
Set/Clear Target Mode, Select With AT N, or Wait
for Reselect. Figure 6-3 illustrates the register bit
values that represent an I/O instruction.
First Dword
Bits 31-30 Instruction Type - I/O Instruction
Bits 29-27 Op Code
T he following Op Code bits have different
meanings, depending on whether the
SYM53C810A is operating in initiator or tar-
get mode. Note: Op Code selections 101-111
are considered Read/Write instructions, and
are described in that section.
Target Mode
Reselect Instruction
1. T he SYM53C810A arbitrates for the SCSI bus
by asserting the SCSI ID stored in the SCID
register. If the SYM53C810A loses arbitration,
then it tries again during the next available
arbitration cycle without reporting any lost
arbitration status.
2. If the SYM53C810A wins arbitration, it
attempts to reselect the SCSI device whose ID
is defined in the destination ID field of the
instruction. Once the SYM53C810A has won
arbitration, it fetches the next instruction from
the address pointed to by the DSP register.
OPC2
OPC1
OPC0
Instruction Defined
0
0
0
0
1
0
0
1
1
0
0
1
0
1
0
Reselect
Disconnect
Wait Select
Set
Clear