SCSI Functional Description
2-41
SCRIPTS instruction has an alternate address to which the SCRIPTS will
jump when this situation occurs. The analogous situation for target
devices is being selected while trying to perform a reselection.
Once a change in operating mode occurs, either the initiator SCRIPTS
issues a Set Initiator instruction or the target SCRIPTS issues a Set
Target instruction. The Selection and Reselection Enable bits (
bits 5 and 6, respectively) should both be asserted, enabling
the LSI53C1000 to respond as an initiator or as a target. If only selection
is enabled, the LSI53C1000 cannot be reselected as an initiator. Status
bits, in the
SCSI Interrupt Status Zero (SIST0)
register, and interrupt bits,
in the
SCSI Interrupt Enable Zero (SIEN0)
register, indicate if the
LSI53C1000 has been selected or reselected.
2.2.15 Synchronous Operation
The LSI53C1000 can transfer synchronous SCSI data in both the initiator
and target modes. The LSI53C1000’s SCLK input must be connected to
a 40 MHz oscillator. The
register controls the
synchronous offset while the
register
controls the synchronous clock converters. These registers may be
loaded by the CPU before SCRIPTS execution begins, from within
SCRIPTS, with a Table Indirect I/O instruction, or with a Read-Modify-
Write instruction.
The LSI53C1000 can receive data from the SCSI bus at a synchronous
transfer period as short as 12.5 ns, regardless of the transfer period used
to send data. The LSI53C1000 can receive data at one-fourth of the
divided SCLK frequency. Depending on the SCLK frequency, the
negotiated transfer period, and the synchronous clock divider, the
LSI53C1000 can send synchronous data at intervals as short as
12.5 ns for Ultra160 SCSI, 25 ns for Ultra2 SCSI, 50 ns for Ultra SCSI,
100 ns for Fast SCSI, and 200 ns for SCSI-1.
Synchronous data transfer rates are controlled by bits in two different
registers of the LSI53C1000. Following is a brief description of these bits
and the method used to determine the data transfer rate.
Содержание LSI53C1000
Страница 6: ...vi Preface...
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Страница 234: ...4 124 Registers...
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Страница 350: ...6 76 Specifications Figure 6 42 LSI53C1000 329 Ball Grid Array Bottom view...
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Страница 360: ...A 8 Register Summary...
Страница 376: ...IX 12 Index...