LSI 53C875A technical manual 3 64-Bit Addressing in Scripts, Hardware Control of Scsi Activity LED

2.2.3 64-Bit Addressing in SCRIPTS

The LSI53C875A has a 32-bit PCI interface which provides 64-bit address capability in the initiator mode.

DACs can be generated for all SCRIPTS operations. There are six selector registers which hold the upper Dword of a 64-bit address. All but one of these is static and requires manual loading using a CPU access, a Load/Store instruction, or a Memory Move instruction. One of the selector registers is dynamic and is used during 64-bit direct block moves only. All selectors default to zero, meaning the LSI53C875A powers-up in a state where only Single Address Cycles (SACs) are generated. When any of the selector registers are written to a nonzero value, DACs are generated.

Direct, Table Indirect and Indirect Block moves, Memory-to-Memory Moves, Load and Store instructions, and jumps are all instructions with 64-bit address capability.

Crossing the 4 Gbyte boundary on any one SCRIPTS operation is not permitted and software needs to take care that any given SCRIPTS operation will not cross the 4 Gbyte boundary.

2.2.4 Hardware Control of SCSI Activity LED

The LSI53C875A has the ability to control a LED through the GPIO_0 pin to indicate that it is connected to the SCSI bus. Formerly this function was done by a software driver.

When bit 5 (LED_CNTL) in the General Purpose Pin Control Zero (GPCNTL0) register is set and bit 6 (Fetch Enable) in the General Purpose Pin Control Zero (GPCNTL0) register is cleared and the LSI53C875A is not performing an EEPROM autodownload, then bit 3 (CON) in the Interrupt Status Zero (ISTAT0) register is presented at the GPIO_0 pin.

The CON (Connected) bit in Interrupt Status Zero (ISTAT0) is set anytime the LSI53C875A is connected to the SCSI bus either as an initiator or a target. This will happen after the LSI53C875A has successfully completed a selection or when it has successfully responded to a selection or reselection. It will also be set when the LSI53C875A wins arbitration in low level mode.

SCSI Functional Description 2-19