Scsi transfer (sxfer), Register: 0x05 – LSI 53C875A User Manual
Page 123
SCSI Registers
4-31
Register: 0x05
SCSI Transfer (SXFER)
Read/Write
Note:
When using Table Indirect I/O commands, bits [7:0] of this
register are loaded from the I/O data structure.
TP[2:0]
SCSI Synchronous Transfer Period
[7:5]
These bits determine the SCSI synchronous transfer
period used by the LSI53C875A when sending
synchronous SCSI data in either the initiator or target
mode. These bits control the programmable dividers in
the chip.
The synchronous transfer period the LSI53C875A should
use when transferring SCSI data is determined in the
following example:
The LSI53C875A is connected to a hard disk which can
transfer data at 10 Mbytes/s synchronously. The
LSI53C875A’s SCLK is running at 40 MHz. The
synchronous transfer period (
) is
found as follows:
SXFERP = Period/SSCP + ExtCC
Period = 1
÷
Frequency = 1
÷
10 Mbytes/s = 100 ns
SSCP = 1
÷
=
SSCF = 1
÷
40 MHz = 25 ns
7
5
4
0
TP[2:0]
MO[4:0]
0
0
0
0
0
0
0
0
TP2
TP1
TP0
XFERP
0
0
0
4
0
0
1
5
0
1
0
6
0
1
1
7
1
0
0
8
1
0
1
9
1
1
0
10
1
1
1
11