Register: 0x49

SCSI Timer One (STIME1)

Read/Write

7

 

6

5

4

 

3

 

 

 

 

 

0

R

 

HTHBA

GENSF

HTHSF

 

 

 

GEN[3:0]

 

 

 

x

 

0

0

0

 

0

 

0

 

0

 

0

R

Reserved

 

 

 

 

 

 

 

 

7

HTHBA

Handshake-to-Handshake Timer Bus Activity

 

 

 

Enable

 

 

 

 

 

 

 

 

6

 

 

Setting this bit causes this timer to begin testing for SCSI

 

 

REQ/, ACK/ activity as soon as SBSY/ is asserted,

 

 

 

regardless of the agents participating in the transfer.

GENSF

General Purpose Timer Scale Factor

 

 

5

 

 

Setting this bit causes this timer to shift by a factor of 16.

 

 

Refer to the SCSI Timer Zero (STIME0) register

 

 

 

description for details.

 

 

 

 

 

 

 

HTHSF

Handshake-to-Handshake Timer Scale Factor

4

 

 

Setting this bit causes this timer to shift by a factor of 16.

 

 

Refer to the SCSI Timer Zero (STIME0) register

 

 

 

description for details.

 

 

 

 

 

 

 

GEN[3:0]

General Purpose Timer Period

 

 

 

 

[3:0]

 

 

These bits select the period of the general purpose timer.

 

 

The time measured is the time between enabling and

 

 

disabling of the timer. When this timing is exceeded, the

 

 

GEN bit in the SCSI Interrupt Status One (SIST1) register

 

 

is set. Refer to the table under SCSI Timer Zero

 

 

 

(STIME0), bits [3:0], for the available time-out periods.

Note: To reset a timer before it expires and obtain repeatable delays, the time value must be written to zero first, and then written back to the desired value. This is also required when changing from one time value to another.

SCSI Registers

4-85

Page 177
Image 177
LSI 53C875A technical manual Hthba, Gensf, Hthsf