LEDC

LED_CNTL

5

 

The internal connected signal (bit 3 of the Interrupt Status

 

Zero (ISTAT0) register) will be presented on GPIO0 if this

 

bit is set and bit 6 of GPCNTL0 is cleared and the chip

 

is not in progress of performing an EEPROM

 

 

autodownload regardless of the state of bit 0 (GPIO0).

 

 

This provides a hardware solution to driving a SCSI

 

 

activity LED in many implementations of LSI Logic SCSI

 

chips.

 

GPIO

GPIO Enable

[4:2]

 

General purpose control, corresponding to bits [4:2] in

 

the GPREG0 register and pins GPIO[4:2]. GPIO4 powers

 

up as a general purpose output, and GPIO[3:2] power-up

 

as general purpose inputs.

 

GPIOGPIO Enable[1:0]

These bits power-up set, causing the GPIO1 and GPIO0 pins to become inputs. Clearing these bits causes GPIO[1:0] to become outputs.

Register: 0x48

SCSI Timer Zero (STIME0)

Read/Write

7

 

 

 

 

4

3

 

 

 

0

 

 

 

HTH[3:0]

 

 

SEL[3:0]

 

 

 

 

 

 

 

 

 

 

 

 

 

0

 

0

 

0

0

0

0

 

0

0

 

 

 

 

 

 

 

 

 

 

 

HTH[3:0]

 

Handshake-to-HandshakeTimer Period

 

[7:4]

These bits select the handshake-to-handshake time-out period, the maximum time between SCSI handshakes (SREQ/ to SREQ/ in target mode, or SACK/ to SACK/ in initiator mode). When this timing is exceeded, an interrupt is generated and the HTH bit in the SCSI Interrupt Status One (SIST1) register is set. The following table contains time-out periods for the Handshake-to-Handshake Timer, the Selection/Reselection Timer (bits [3:0]), and the General Purpose Timer (SCSI Timer One (STIME1) bits [3:0]). For a more detailed explanation of interrupts, refer to Chapter 2, “Functional Description.”

SCSI Registers

4-83

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LSI 53C875A technical manual Ledc Ledcntl, Gpio Enable, Gpiogpio Enable10, Scsi Timer Zero STIME0 Read/Write