STPC12GEYI datasheet(21/111 Pages) STMICROELECTRONICS

21 / 111 page

PIN DESCRIPTION

Issue 1.0 - July 24, 2002

21/111

the STPC Atlas. The STPC Atlas monitors this

signal as an input when performing an ISA cycle

on behalf of the host CPU, DMA master or refresh.

ISA masters which do not monitor IOCHRDY are

not guaranteed to work with the STPC Atlas since

the access to the system memory can be

considerably delayed due to CRT refresh or a

write back cycle.

ALE

Address Latch Enable. This is the address

latch enable output of the ISA bus and is asserted

by the STPC Atlas to indicate that LA23-17, SA19-

0, AEN and SBHE# signals are valid. The ALE is

driven high during refresh, DMA master or an ISA

master cycles by the STPC Atlas.

ALE is driven low after reset.

BHE#

System Bus High Enable. This signal, when

asserted, indicates that a data Byte is being

transferred on SD15-8 lines. It is used as an input

when an ISA master owns the bus and is an

output at all other times.

MEMR#

Memory Read. This is the memory read

command signal of the ISA bus. It is used as an

input when an ISA master owns the bus and is an

output at all other times.

The MEMR# signal is active during refresh.

MEMW#

Memory Write. This is the memory write

command signal of the ISA bus. It is used as an

input when an ISA master owns the bus and is an

output at all other times.

SMEMR# System Memory Read. The STPC Atlas

generates SMEMR# signal of the ISA bus only

when the address is below one MByte or the cycle

is a refresh cycle.

SMEMW# System Memory Write. The STPC

Atlas generates SMEMW# signal of the ISA bus

only when the address is below one MByte.

IOR# I/O Read. This is the IO read command

signal of the ISA bus. It is an input when an ISA

master owns the bus and is an output at all other

times.

IOW# I/O Write. This is the IO write command

signal of the ISA bus. It is an input when an ISA

master owns the bus and is an output at all other

times.

MASTER#

Add On Card Owns Bus. This signal is

active when an ISA device has been granted bus

ownership.

MCS16# Memory Chip Select16. This is the

decode of LA23-17 address pins of the ISA

address bus without any qualification of the

command signal lines. MCS16# is always an

input. The STPC Atlas ignores this signal during

IO and refresh cycles.

IOCS16#

IO Chip Select16. This signal is the

decode of SA15-0 address pins of the ISA

address bus without any qualification of the

command signals. The STPC Atlas does not drive

IOCS16# (similar to PC-AT design). An ISA

master access to an internal register of the STPC

Atlas is executed as an extended 8-bit IO cycle.

REF#

Refresh Cycle. This is the refresh command

signal of the ISA bus. It is driven as an output

when the STPC Atlas performs a refresh cycle on

the ISA bus. It is used as an input when an ISA

master owns the bus and is used to trigger a

refresh cycle.

The STPC Atlas performs a pseudo hidden

refresh. It requests the host bus for two host

clocks to drive the refresh address and capture it

external

buffers.

The

host bus

then

relinquished while the refresh cycle continues on

the ISA bus.

AEN

Address Enable. Address Enable is enabled

when the DMA controller is the bus owner to

indicate that a DMA transfer will occur. The

enabling of the signal indicates to IO devices to

ignore

the

IOR#/IOW#

signal

during

DMA

transfers.

IOCHCK#

IO Channel Check. IO Channel Check

is enabled by any ISA device to signal an error

condition that can not be corrected. NMI signal

becomes active upon seeing IOCHCK# active if

the corresponding bit in Port B is enabled.

GPIOCS#

I/O General Purpose Chip Select 1.

This output signal is used by the external latch on

ISA bus to latch the data on the SD[7:0] bus. The

latch can be use by PMU unit to control the

external peripheral devices to power down or any

other desired function.

RTCRW#

Real Time Clock RW#. This pin is used

as RTCRW#. This signal is asserted for any I/O

write to port 71h.

RTCDS# Real Time Clock DS. This pin is used as

RTCDS#. This signal is asserted for any I/O read

to port 71h. Its polarity complies with the DS pin of

the MT48T86 RTC device when configured with

Intel timings.

RTCAS

Real time clock address strobe. This

signal is asserted for any I/O write to port 70h.

RMRTCCS# ROM/Real Time clock chip select.

This pin is a multi-function pin. This signal is

asserted if a ROM access is decoded during a

memory cycle. It should be combined with

MEMR# or MEMW# signals to properly access the

ROM. During an IO cycle, this signal is asserted if

access to the Real Time Clock (RTC) is decoded.

It should be combined with IOR# or IOW# signals

to properly access the real time clock.

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