82371AB (PIIX4)
E
22
4/9/97 2:23 PM PIIX4aDS
INTEL CONFIDENTIAL
(until publication date)
PRELIMINARY
Name
Type
Description
RTCALE/
GPO25
O
REAL TIME CLOCK ADDRESS LATCH ENABLE.
RTCALE is used to latch the
appropriate memory address into the RTC. A write to port 70h with the appropriate RTC
memory address that will be written to or read from causes RTCALE to be asserted.
RTCALE is asserted on falling IOW# and remains asserted for two SYSCLKs.
If the internal Real Time Clock is used, this signal can be programmed as a general
purpose output.
During Reset:
Low
After Reset:
Low
During POS:
Low/GPO
RTCCS#/
GPO24
O
REAL TIME CLOCK CHIP SELECT.
RTCCS# is asserted during read or write I/O
accesses to RTC location 71h. RTCCS# can be tied to a pair of external OR gates to
generate the real time clock read and write command signals. If the internal Real Time
Clock is used, this signal can be programmed as a general purpose output.
During Reset:
High
After Reset:
High
During POS:
High/GPO
XDIR#/
GPO22
O
X-BUS TRANSCEIVER DIRECTION.
XDIR# is tied directly to the direction control of a
74’245 that buffers the X-Bus data, XD[7:0]. XDIR# is asserted (driven low) for all I/O
read cycles regardless if the accesses is to a PIIX4 supported device. XDIR# is
asserted for memory cycles only if BIOS or APIC space has been decoded. For PCI
master initiated read cycles, XDIR# is asserted from the falling edge of either IOR# or
MEMR# (from MEMR# only if BIOS or APIC
space has been decoded), depending on
the cycle type. For ISA master-initiated read cycles, XDIR# is asserted from the falling
edge of either IOR# or MEMR# (from MEMR# only if BIOS space has been decoded),
depending on the cycle type. When the rising edge of IOR# or MEMR# occurs, PIIX4
negates XDIR#. For DMA read cycles from the X-Bus, XDIR# is driven low from
DACKx# falling and negated from DACKx# rising. At all other times, XDIR# is negated
high.
If the X-Bus not used, then this signal can be programmed to be a general purpose
output.
During Reset:
High
After Reset:
High
During POS:
High
/
GPO
XOE#/
GPO23
O
X-BUS TRANSCEIVER OUTPUT ENABLE.
XOE# is tied directly to the output enable
of a 74’245 that buffers the X-Bus data, XD[7:0], from the system data bus, SD[7:0].
XOE# is asserted anytime a PIIX4 supported X-Bus device is decoded, and the devices
decode is enabled in the X-Bus Chip Select Enable Register (BIOSCS#, KBCCS#,
RTCCS#, MCCS#) or the Device Resource B (PCCS0#) and Device Resource C
(PCCS1#). XOE# is asserted from the falling edge of the ISA commands (IOR#, IOW#,
MEMR#, or MEMW#) for PCI Master and ISA master-initiated cycles. XOE# is negated
from the rising edge of the ISA command signals for PCI Master initiated cycles and the
SA[16:0] and LA[23:17] address for ISA master-initiated cycles. XOE# is not generated
during any access to an X-Bus peripheral in which its decode space has been disabled.
If an X-Bus not used, then this signal can be programmed to be a general purpose
output.
During Reset:
High
After Reset:
High
During POS:
High
/
GPO