(This SCSI synchronous core clock is determined in SCNTL3 bits [6:4], ExtCC = 1 if SCNTL1 bit 7 is asserted and the LSI53C875A is sending data. ExtCC = 0 if the LSI53C875A is receiving data.)

SXFERP = 100 25 = 4

Where:

SXFERP Synchronous transfer period.

SSCP SCSI synchronous core period.

SSCF SCSI synchronous core frequency.

ExtCC Extra clock cycle of data setup.

Table 4.3 shows examples of synchronous transfer periods and rates for SCSI-1.

Table 4.3 Examples of Synchronous Transfer Periods and Rates for SCSI-1

 

SCSI CLK

XFERP

Synch.

Synch.

CLK (MHz)

SCNTL3

(SXFER

Transfer

Transfer Rate

Bits [6:4]

Bits [7:5])

Period (ns)

(Mbytes/s)

 

 

 

 

 

66.67

3

4

180

5.55

 

 

 

 

 

66.67

3

5

225

4.44

 

 

 

 

 

50

2

4

160

6.25

 

 

 

 

 

50

2

5

200

5

 

 

 

 

 

40

2

4

200

5

 

 

 

 

 

37.50

1.5

4

160

6.25

 

 

 

 

 

33.33

1.5

4

180

5.55

 

 

 

 

 

25

1

4

160

6.25

 

 

 

 

 

20

1

4

200

5

 

 

 

 

 

16.67

1

4

240

4.17

 

 

 

 

 

4-32Registers

Page 124
Image 124
LSI 53C875A technical manual Synch CLK MHz, Transfer Rate, Bits Period ns Mbytes/s