Table 4.4 shows example transfer periods and rates for fast SCSI-2 and Ultra SCSI.

Table 4.4 Example Transfer Periods and Rates for Fast SCSI-2 and Ultra SCSI

 

SCSI CLK

 

Synch.

Synch. Transfer

 

SCNTL3

 

Transfer

Rate

CLK (MHz)

Bits [6:4]

XFERP

Period (ns)

(Mbytes/s)

 

 

 

 

 

1601

2

4

50

20

 

 

 

 

 

1601

4

4

100

10

80

1

4

50

20

 

 

 

 

 

50

1

4

80

12.5

 

 

 

 

 

50

1

5

100

10.0

 

 

 

 

 

40

1

4

100

10.0

 

 

 

 

 

37.50

1

4

106.67

9.375

 

 

 

 

 

33.33

1

4

120

8.33

 

 

 

 

 

25

1

4

160

6.25

 

 

 

 

 

20

1

4

200

5

 

 

 

 

 

16.67

1

4

240

4.17

 

 

 

 

 

1. Only with 40 MHz clock.

 

MO[4:0]

Max SCSI Synchronous Offset

[4:0]

These bits describe the maximum SCSI synchronous offset used by the LSI53C875A when transferring synchronous SCSI data in either the initiator or target mode. Table 4.5 describes the possible combinations and their relationship to the synchronous data offset used by the LSI53C875A. These bits determine the LSI53C875A’s method of transfer for Data-In and Data-Out phases only; all other information transfers occur asynchronously.

SCSI Registers

4-33

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LSI 53C875A technical manual MO40 Max Scsi Synchronous Offset