LSI LSI53C1000, Technical Manual

Page: 73 / 384

SCSI Functional Description 2-45
Figure 2.5 Determining the Synchronous Transfer Rate
2.2.16 Interrupt Handling
The SCRIPTS processor in the LSI53C1000 performs most functions
independently of the host microprocessor. However, certain interrupt
situations must be handled by the external microprocessor. This section
explains all aspects of interrupts as they apply to the LSI53C1000.
2.2.16.1 Polling and Hardware Interrupts
The external microprocessor is informed of an interrupt condition by
polling or hardware interrupts. Polling means that the microprocessor
must continually loop and read a register until it detects a bit that is set
40 MHz
Clock
Quadrupler
SCF
Divider
Asynchronous
Divider
Asynchronous
SCSI Logic
Divide by 4 (ST)
SCF2 SCF1 SCF0 SCF Divisor
0 0 0 3
0 0 1 1
0 1 0 1.5
0 1 1 2
1 0 0 3
1 0 1 4
1 1 0 6
Receive/Send
Divide by 2 (DT)
SCLK
Rate
Received Rate (DT)
Input Clock Rate
SCF Divisor 2
× ( )
---------------------------------------------- (Megatransfers/s) =
Receive Rate (ST)
Input Clock Rate
SCF Divisor 4
× ( )
---------------------------------------------- (Megatransfers/s) =
Send Rate (DT)
Input Clock Rate
SCF Divisor 2
XCLKS_DT XCLKS_ST XCLKH_DT XCLKH_ST + + +
2
----------------------------------------------------------------------------------------------------------------------------------------------- +
 
 
×
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- =
Send Rate (ST)
Input Clock Rate
SCF Divisor 4 XCLKS_ST XCLKH_ST
+ +
( ) ×
------------------------------------------------------------------------------------------------------------------------- =