82375EB datasheet(47/131 Pages) INTEL

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82375EBSB

Bit

Description

152

BIOS Timer Base Address

Bits 152 correspond to PCI address lines AD 152

Reserved

BIOS Timer Enable (BTE)

When BTEe1 the BIOS Timer is enabled When BTEe0 the BIOS

Timer is disabled The default is 0 (disabled)

3126 ELTCREISA LATENCY TIMER CONTROL REGISTER

Address Offset

84h

Default value

7Fh

Attribute

ReadWrite

Size

8 bits

This register provides the control for the EISA Latency Timer (ELT) The register holds the initial count value

used by the ELT The ELT uses the PCI clock for counting The ELT time-out period is equal to

ELTtimeouteValue ELTCR(70) xTpciclck ns

where

Tpciclke30 ns at 33 MHz (40 ns at 25 MHz)

Therefore a maximum ELT time-out period at 33 MHz is 256 x 30 ns e 768 ms The value written into this

Latency Timer mechanism and on EISA Bus arbitrationlatency parametrics A typical value corresponds to

the ELT time-out period of 1 – 3 ms When the value in the ELTCR Register is 0 the ELT mechanism is

disabled The ELTCR Register must be initialized before EISA masters or DMA are enabled

Bit

Description

EISA Latency Timer Count Value

Bits 70 contain the initial count value for the EISA Latency

Timer When this field contains 00h the EISA Latency Timer is disabled

32 IO Registers

The only PCEB internal resource mapped to the PCI IO space is the BIOS Timer Register

321 BIOSTMBIOS TIMER REGISTER

Programmable IO address location (Dword aligned)

Default Value

00 00 xx xxh

Attribute

ReadWrite

Size

32 bits

This 32-bit register is mapped to the PCI IO space location determined by the value in the BTMR Register Bit

0 of BTMR must be 1 to enable access to the BIOS Timer The BIOS timer clock is derived from the EISA Bus

clock (BCLK) either 825 or 833 MHz depending on the PCI clock BCLK is divided by 8 to obtain the timer

clock of 103 or 104 MHz If a frequency other than 33 MHz or 25 MHz is used for PCI clock the BIOS Timer

clock will be affected (It will always keep the same relation to the BCLK ie 14 or 13 depending on the clock

divisor) The BIOS Timer is only accessible from the PCI Bus and is not accessible from the EISA Bus

82375EB датащи(PDF) 47 Page - Intel Corporation

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