SSM

Single Step Mode

4

 

Setting this bit causes the LSI53C810A to stop after

 

 

executing each SCRIPTS instruction, and generate a

 

 

single step interrupt. When this bit is cleared the

 

 

LSI53C810A does not stop after each instruction. It

 

 

continues fetching and executing instructions until an

 

 

interrupt condition occurs. For normal SCSI SCRIPTS

 

 

operation, keep this bit clear. To restart the LSI53C810A

 

after it generates a SCRIPTS Step interrupt, read the

 

 

Interrupt Status (ISTAT) and DMA Status (DSTAT)

 

 

registers to recognize and clear the interrupt. Then set

 

 

the START DMA bit in this register.

 

IRQM

IRQ Mode

3

 

When set, this bit enables a totem pole driver for the IRQ

 

pin. When reset, this bit enables an open drain driver for

 

the IRQ pin with a internal weak pull-up. This bit is reset

 

at power-up.

 

STD

Start DMA Operation

2

 

The LSI53C810A fetches a SCSI SCRIPTS instruction

 

 

from the address contained in the DMA SCRIPTS Pointer

 

(DSP) register when this bit is set. This bit is required if

 

the LSI53C810A is in one of the following modes:

 

 

Manual start mode – Bit 0 in the DMA Mode

 

 

(DMODE) register is set

 

 

Single step mode – Bit 4 in the DMA Control (DCNTL)

 

register is set

 

 

When the LSI53C810A is executing SCRIPTS in manual

 

start mode, the Start DMA bit needs to be set to start

 

 

instruction fetches. This bit remains set until an interrupt

 

occurs. When the LSI53C810A is in single step mode, set

 

the Start DMA bit to restart execution of SCRIPTS after

 

a single step interrupt.

 

IRQD

IRQ Disable

1

 

Setting this bit 3-states the IRQ pin. Clearing the bit

 

 

enables normal operation. When bit 1 in this register is

 

set, the IRQ/ pin is not asserted when an interrupt condition occurs. The interrupt is not lost or ignored, but merely masked at the pin. Clearing this bit when an interrupt is pending immediately causes the IRQ/ pin to

5-46

Operating Registers

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LSI 53C810A technical manual Ssm, Irqm, Std, Irqd