3.2 Signal Descriptions

The Signal Descriptions are divided into PCI Bus Interface Signals, SCSI Bus Interface Signals, GPIO Signals, ROM Flash and Memory Interface Signals, Test Interface Signals, and Power and Ground Signals.

The PCI Bus Interface Signals are subdivided into System Signals, Address and Data Signals, Interface Control Signals, Arbitration Signals, Error Reporting Signals, and Interrupt Signal.

The SCSI Bus Interface Signals are subdivided into SCSI Bus Interface Signals, SCSI Signals, and SCSI Control Signals.

Signals are assigned a type. There are five signal types:

IInput, a standard input only signal.

OOutput, a standard output driver (typically a Totem Pole Output).

I/O Input and output (bidirectional).

T/S 3-state, a bidirectional, 3-state input/output signal.

S/T/S Sustained 3-state, an active LOW 3-state signal owned and driven by one and only one agent at a time.

3.2.1 Internal Pull-ups on LSI53C875A Signals

Several signals in the LSI53C875A have internal pull-up resistors.

Table 3.1 describes the conditions that enable these pull-ups.

Table 3.1

LSI53C875A Internal Pull-ups

 

 

 

 

Signal Name

 

Pull-up Current

Conditions for Pull-up

 

 

 

 

IRQ/

 

25 A

Pull-up enabled when the IRQ mode bit (bit 3 of DCNTL

 

 

 

(0x3B)) is cleared.

 

 

 

 

GPIO[1:0]

 

25 A

Pull-up enabled when bits [1:0] of General Purpose Pin

 

 

 

Control Zero (GPCNTL0) are not set.

 

 

 

 

TEST_HSC/

 

25 A

Pull-up enabled all the time.

 

 

 

 

TEST_RST/

 

25 A

Pull-up enabled all the time.

 

 

 

TRST, TCK, TMS, TDI

25 A

Pull-up enabled all the time.

 

 

 

 

Signal Descriptions

3-3

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LSI technical manual Signal Descriptions, Internal Pull-ups on LSI53C875A Signals, LSI53C875A Internal Pull-ups