STPC STMicroelectronics, STPC Datasheet - Page 18

• Manufacturer Part Number: STPC
• Description: PC Compatible Embeded Microprocessor
• Manufacturer: STMicroelectronics

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PIN DESCRIPTION
2.2.7 ISA/IDE COMBINED CONTROL
IOCHRDY/DIORDY Channel Ready (ISA)/Busy/
Ready (IDE). This is a multi-function pin. When
the ISA bus is active, this pin is IOCHRDY. When
the IDE bus is active, this serves as IDE signal DI-
ORDY.
IOCHRDY is the IO channel ready signal of the
ISA bus and is driven as an output in response to
an ISA master cycle targeted to the host bus or an
internal register of the STPC Consumer. The
STPC Consumer 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 Consumer
since the access to the system memory can be
considerably delayed due to CRT refresh or a
write back cycle.
2.2.8 ISA CONTROL
ALE Address Latch Enable. This is the address
latch enable output of the ISA bus and is asserted
by the STPC Consumer 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 Consumer.
ALE is driven low after reset.
BHE# System Bus High Enable. This signal, when
asserted, indicates that a data byte is being trans-
ferred 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 in-
put 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 in-
put when an ISA master owns the bus and is an
output at all other times.
SMEMR# System Memory Read. The STPC Con-
sumer generates SMEMR# signal of the ISA bus
only when the address is below one megabyte or
the cycle is a refresh cycle.
SMEMW# System Memory Write. The STPC Con-
sumer generates SMEMW# signal of the ISA bus
only when the address is below one megabyte.
This signal is multiplexed with COL_CMP on the
VGA Interface. The signal is selected by setting
Strap Option MD[0] as described in Section 3.
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Issue 1.2
IOR# I/O Read. This is the IO read command sig-
nal of the ISA bus. It is an input when an ISA mas-
ter owns the bus and is an output at all other
times.
IOW# I/O Write. This is the IO write command sig-
nal of the ISA bus. It is an input when an ISA mas-
ter 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 de-
code of LA23-17 address pins of the ISA address
bus without any qualification of the command sig-
nal lines. MCS16# is always an input. The STPC
Consumer ignores this signal during IO and re-
fresh cycles.
IOCS16# IO Chip Select16. This signal is the de-
code of SA15-0 address pins of the ISA address
bus without any qualification of the command sig-
nals. The STPC Consumer does not drive
IOCS16# (similar to PC-AT design). An ISA mas-
ter access to an internal register of the STPC Con-
sumer 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 Consumer performs a refresh cy-
cle 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 Consumer performs a pseudo hidden
refresh. It requests the host bus for two host
clocks to drive the refresh address and capture it
in external buffers. The host bus is then relin-
quished 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 indi-
cate that a DMA transfer will occur. The enabling
of the signal indicates to IO devices to ignore the
IOR#/IOW# signal during DMA transfers.
ZWS# Zero Wait State. This signal, when assert-
ed by addressed device, indicates that current cy-
cle can be shortened.
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 be-
comes active upon seeing IOCHCK# active if the
corresponding bit in Port B is enabled.